Problem with package references in java/kotlin project

I created a gradle project with java/kotlin jvm.

The package structure is

com.rsk.kotlin, for kotlin src

com.rsk.java, for java src

Everything looks good in pro structure, and I get no syntax errors in the editor, but I'm getting a compile error, "Unresolved reference: java" referring to rsk.com.java.

I tried 'Invalidate Caches / Restart' and it didn't help.

Any 'Ideas'?