'Unresolved reference' errors for android library module referenced in app module

I have problems referencing my android library modules in my projects. Beside the main app module I use to have an android library module with either util stuff or as data module. I reference it in app module like that:

dependencies {
implementation project(":data")
}

When I build the project, it´s giving me lot of error messages `'Unresolved reference: ...'` for all stuff that I reference in the app module to the android library module. But the IDE itself doesn´t have a problem, Intelligent finds all classes, interfaces etc., imports are fine, nothing is red. The android library module itself builds and creates `aar-file` in the output. It´s the `compileDebugKotlin` task that fails

Any general idea what may be related to that?

Found the problem, my android library module was missing the kotlin configuration:

apply plugin: 'kotlin-android'

dependencies {
implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlinVersion:<version>"
}

Although I used kotlin .kt files in it, it could build without and also

`Tools -> Kotlin -> 'Configure Kotlin in projects'`

had told me **'All modules with Kotlin files are configured'**

Your module's `build.gradle` file should have:

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

dependencies {
...
implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
...
}

If it is a ```kotlin``` module make sure to add in its `build.gradle` file

`apply plugin: 'kotlin'`

In my case It was `apply plugin: 'kotlin-android'`,

implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
and also added it on build.gradle

androidExtensions {
experimental = true
}

I was using CoroutineWorkers and in my case I had to add **work-runtime-ktx** dependency to use it

implementation "androidx.work:work-runtime-ktx:2.4.0"