Scala can't compile whenever I upgrade IntelliJ

I've had this problem every time I've upgraded IDEA for the last year and a half. Before that I never used Scala. So what I find is that the Scala components of the project can't compile due to some mysterious error, whereas the maven build works just fine. This morning I upgraded to 2018.1 and have been unable to compile ever since. My usual solution is to muck around for about a day until it mysteriously gets better, but that gets old. This is JDK 1.7.0_80, Scala 2.9.2, IntelliJ 2018.1.

When I compile, the Build tab says this:

Information:javac 7 was used to compile java sources
Information:23/05/18 2:04 PM - Compilation completed with 1 error and 0 warnings in 10 s 27 ms
Error:Module 'redacted' production: sbt.internal.inc.CompileFailed

That's all. Module redacted depends on two other modules which contain no Scala code. Module redacted includes only one Scala file, in the test sources, which depends on code from the Java modules. The Scala errors in the idea.log below are not from my code.

pom.xml for the module:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>au.com.redacted</groupId>
<artifactId>redacted</artifactId>
<version>2.8.4-SNAPSHOT</version>
</parent>
<artifactId>redacted</artifactId>
<name>redacted</name>
<packaging>jar</packaging>
<dependencies>

<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-orm</artifactId>
<version>${spring.version}</version>
</dependency>

<... redacted ...>

<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.29</version>
</dependency>
<dependency>
<groupId>net.sf.ehcache</groupId>
<artifactId>ehcache</artifactId>
<version>1.5.0</version>
</dependency>
<dependency>
<groupId>commons-logging</groupId>
<artifactId>commons-logging</artifactId>
<version>1.1.1</version>
</dependency>
<dependency>
<groupId>commons-collections</groupId>
<artifactId>commons-collections</artifactId>
<version>3.2.1</version>
</dependency>
<dependency>
<groupId>commons-fileupload</groupId>
<artifactId>commons-fileupload</artifactId>
<version>1.2.1</version>
</dependency>

<!-- AD: I haven't investigated but this dep gets blocked. It's pretty important and caused a live bug for not being included. -->
<dependency>
<groupId>org.jadira.usertype</groupId>
<artifactId>usertype.spi</artifactId>
<version>1.8</version>
</dependency>

<dependency>
<groupId>org.elasticsearch</groupId>
<artifactId>elasticsearch</artifactId>
<version>1.2.1</version>
</dependency>

</dependencies>
<build>
<plugins>
<!-- SCALA -->
<plugin>
<groupId>org.scala-tools</groupId>
<artifactId>maven-scala-plugin</artifactId>
<version>2.15.2</version>
<configuration>
<charset>${project.build.sourceEncoding}</charset>
<jvmArgs>
<jvmArg>-Xmx1024m</jvmArg>
<jvmArg>-DpackageLinkDefs=file://${project.build.directory}/packageLinkDefs.properties</jvmArg>
</jvmArgs>
</configuration>
<executions>
<execution>
<goals>
<goal>compile</goal>
<goal>testCompile</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

idea.log:

2018-05-23 14:02:48,129 [4396272] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stdout]: Build process started. Classpath: /home/john/bin/idea-IU-181.5087.20/lib/jps-launcher.jar:/home/john/bin/idea-IU-181.5087.20/jre64/lib/tools.jar:/home/john/bin/idea-IU-181.5087.20/lib/optimizedFileManager.jar
2018-05-23 14:02:48,149 [4396292] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
2018-05-23 14:02:48,149 [4396292] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: SLF4J: Defaulting to no-operation (NOP) logger implementation
2018-05-23 14:02:48,149 [4396292] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
2018-05-23 14:04:39,756 [4507899] INFO - ij.compiler.impl.CompileDriver - COMPILATION STARTED (BUILD PROCESS)
2018-05-23 14:04:40,428 [4508571] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stdout]: Build process started. Classpath: /home/john/bin/idea-IU-181.5087.20/lib/jps-launcher.jar:/home/john/bin/idea-IU-181.5087.20/jre64/lib/tools.jar:/home/john/bin/idea-IU-181.5087.20/lib/optimizedFileManager.jar
2018-05-23 14:04:40,447 [4508590] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
2018-05-23 14:04:40,447 [4508590] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: SLF4J: Defaulting to no-operation (NOP) logger implementation
2018-05-23 14:04:40,447 [4508590] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
2018-05-23 14:04:49,525 [4517668] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/Analyzer.scala:31: error: ')' expected but string literal found.
2018-05-23 14:04:49,527 [4517670] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: assert(sym.isClass, s"${sym.fullName} is not a class")
2018-05-23 14:04:49,527 [4517670] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,568 [4517711] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/CompilerInterface.scala:95: error: ';' expected but string literal found.
2018-05-23 14:04:49,569 [4517712] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: s"[zinc] Running cached compiler $compilerId for Scala compiler $versionString"
2018-05-23 14:04:49,569 [4517712] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,590 [4517733] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/DelegatingReporter.scala:149: error: ';' expected but string literal found.
2018-05-23 14:04:49,590 [4517733] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: override def toString = s"[$severity] $pos: $message"
2018-05-23 14:04:49,590 [4517733] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,650 [4517793] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/ExtractUsedNames.scala:122: error: ';' expected but string literal found.
2018-05-23 14:04:49,651 [4517794] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: val msg = s"The ${unit.source} contains the following used names:\n"
2018-05-23 14:04:49,651 [4517794] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,658 [4517801] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/GlobalHelpers.scala:162: error: ';' expected but string literal found.
2018-05-23 14:04:49,659 [4517802] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: s"The symbol $symbol comes from an unknown source or compiled source -- ignoring."
2018-05-23 14:04:49,659 [4517802] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,659 [4517802] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/GlobalHelpers.scala:164: error: ';' expected but string literal found.
2018-05-23 14:04:49,659 [4517802] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: s"The ${culprit.fullName} defined at ${culprit.fullLocationString} is not a class symbol."
2018-05-23 14:04:49,659 [4517802] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,659 [4517802] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/GlobalHelpers.scala:166: error: ';' expected but string literal found.
2018-05-23 14:04:49,659 [4517802] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: s"No enclosing class. Discarding dependency on $culprit (currentOwner = $owner)."
2018-05-23 14:04:49,659 [4517802] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,659 [4517802] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/GlobalHelpers.scala:167: error: ';' expected but string literal found.
2018-05-23 14:04:49,659 [4517802] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: def noTopLevelMember(found: String) = s"""
2018-05-23 14:04:49,659 [4517802] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/LocalToNonLocalClass.scala:40: error: ')' expected but string literal found.
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: s"Tried to resolve ${s.fullName} to a non local classes but the resolution works up to sbtDependency phase. We're at ${phase.name}"
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/LocalToNonLocalClass.scala:52: error: ')' expected but string literal found.
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: assert(s.isClass, s"The ${s.fullName} is not a class.")
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/LocalToNonLocalClass.scala:57: error: ')' expected but string literal found.
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: assert(s.isClass, s"The ${s.fullName} is not a class.")
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: /home/john/.IntelliJIdea2018.1/system/compile-server/develop_8e89a9a1/_temp_/sbt_20cbe3c4/xsbt/LocalToNonLocalClass.scala:58: error: ';' expected but ')' found.
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: cache.getOrElseUpdate(s, lookupNonLocal(s))
2018-05-23 14:04:49,667 [4517810] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: ^
2018-05-23 14:04:49,681 [4517824] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: 12 errors found
2018-05-23 14:04:49,779 [4517922] INFO - lij.compiler.impl.CompilerUtil - COMPILATION FINISHED (BUILD PROCESS); Errors: 1; warnings: 0 took 10027 ms: 0 min 10sec
2018-05-23 14:04:49,830 [4517973] INFO - s.CompilerReferenceServiceImpl - backward reference index reader is opened
2018-05-23 14:04:50,008 [4518151] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stdout]: Build process started. Classpath: /home/john/bin/idea-IU-181.5087.20/lib/jps-launcher.jar:/home/john/bin/idea-IU-181.5087.20/jre64/lib/tools.jar:/home/john/bin/idea-IU-181.5087.20/lib/optimizedFileManager.jar
2018-05-23 14:04:50,026 [4518169] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
2018-05-23 14:04:50,026 [4518169] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: SLF4J: Defaulting to no-operation (NOP) logger implementation
2018-05-23 14:04:50,026 [4518169] INFO - j.compiler.server.BuildManager - BUILDER_PROCESS [stderr]: SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.