Downgrade
Answered
After upgrading IntelliJ IDEA from version 2017.1.5 to version 2017.2 on a Mac with macOS Sierra 10.12.5, at least the following IDE features weren't functioning in a Java 1.8 multi-module Maven project any more: refactoring (renaming classes), code completion, error highlighting, automatic project builds, find usages, optimize imports. I've just uninstalled 2017.2 and downgraded back to version 2017.1.5.
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Reinstalling 2017.2 from http://www.jetbrains.com/idea/download/index.html should have fixed the problem. You can also try 2017.2.1: https://confluence.jetbrains.com/display/IDEADEV/IDEA+2017.2+EAP,