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There is currently a bug in sbt (Scala Build Tool) version 1.3.0 that interacts poorly with the official Scala plugin for IntelliJ (see SCL-16208). You should use sbt version 1.2.8 (the previous stable version) until a new version is released. The bug has been patched in sbt, so we expect version 1.3.1 and onward will work correctly once available.
Other Options
Using sbt Directly
If you don't like IntelliJ, the second official recommendation from scala-lang.org is to download sbt (Scala Build Tool) directly, then run commands from your shell to build and test your project. If you prefer using Vim or Emacs as your primary editor, this is a good option for you.
Using VSCode + sbt
If you still like the feel of a traditional IDE but IntelliJ feels to heavy-weight, you can also try Microsoft's open source VSCode IDE with its Scala Metals plugin. The plugin gives you syntax highlighting, auto-complete, compiler error highlighting, usage location, etc.; however, it's not as fully-integrated as IntelliJ since you still have to compile and test from the shell by invoking sbt directly.
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