Can't debug my Android library if the class was created with Kotlin

I created an Android library that was originally coded with Java and it outputs an .aar file that I use in some of my projects.

When I include this lib in a project (an Android project created with Kotlin) and I decide to debug the code in this project, when the debugger reaches a line containing a library's class, it successfully steps into the class and I can see the source code of the class while I'm debugging it. I can continue the debug line by line inside the lib's class and everything works as expected.

However, I recently decided to convert this library to Kotlin but now, when the debugger reaches one of the lib's class and I step into the class to continue debugging there, I can no longer see the entire source code. I can only see the method signatures, but without the method definitions. I see only things like:

public class ClassA {
    public fun function1(): kotlin.Unit

    public fun function2(): kotlin.Unit

    public fun function3(): kotlin.Unit
}

I didn't do any else in the library's project settings. I simply converted the files from .java to .kt.

Here are some things that I tried so far to solve this problem:

• I confirmed that I included Kotlin's standard lib in the dependencies list of the build.gradle file in the library.
• I disabled ProGuard (it has never been a problem, but I removed it just in case).
• I disabled code minification (it has never been a problem too, but at this point I'm willing to try anything).

Anyone has any idea why this is happening?