IntelliJ problem with gradle project using scala

I have problem using gradle projects with source code in scala. We recently decided to move from maven to gradle. Initially we converted several projects written in kotlin and it was totally painless from the Idea side. We could open gradle projects in Idea, compile them in Idea and run tests - perfect. Now we have a few projects written in scala - notice those were in maven and worked very well Idea but after conversion to gradle even though projects itself open successfully in Idea (nothing red) the compilation from Idea fails at the compileTestScala and it appears that test classes don't see (at all) classes from main (same module). The gradle build itself has no problems. Do you have any advice? Btw. we tried all obvious steps like cleaning caches, deleting .idea and *.iml reimporting again but problem persist