IntelliJ IDEA: Run / Debug buttons now do not anything for any file.

I am using IntelliJ IDEA 2018.1.2 Community Edition (full details at end of this post)

I have a Scala project which is being compiled with sbt.  Everything has been working fine for the last year, but I now find that when I try to run any executable file, nothing happens.  Previously a "Run" or "Debug" panel appeared at the bottom of the window when I tried running or debugging executables.  Now none of my program files and none of my unit tests will run.  Everything still works fine if I manually execute them from the command line.

I have updated to the most recent version of IntelliJ and restarted and invalidated caches.  Is this a known issue?  I don't get any error messages, it's just nothing happens when anything should be run or debugged.

I am not getting any error messages from IntelliJ, so I do not know how to troubleshoot further.

Full IntelliJ build details are below:

IntelliJ IDEA 2018.1.2 (Community Edition)
Build #IC-181.4668.68, built on April 24, 2018
JRE: 1.8.0_152-release-1136-b29 x86_64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
macOS 10.13.4