Kotlin coroutine support missing

I always get an exception on line 124 of NextcloudRetrofitServiceMethod.invoke():

        // Build/parse dynamic parameters
        for(int i = 0; i < parameterAnnotationsArray.length; i++) {
            Annotation annotation = parameterAnnotationsArray[i][0]; // <----- Blows up

I tried debugging this method, but every time it hits a breakpoint in here the app crashes.

Here's my Retrofit:

interface BookmarkService {

    @GET("bookmark")
    suspend fun getBookmarks(
        @Query("folder") folderId: Int,
        @Query("page") page: Int,
        @Query("tags") tags: List<String>
    ): DtoBookmarks

    @GET("folder?layers=1")
    suspend fun getFolders(
        @Query("root") parentFolderId: Int
    ): DtoFolders
}

These are my dependencies:

    implementation 'com.github.nextcloud:Android-SingleSignOn:0.5.0-rc4'
    implementation 'com.squareup.retrofit2:retrofit:2.6.4'
    implementation 'com.squareup.retrofit2:converter-gson:2.6.4'

Let me know if you need any more info.

Start by reproducing the crash from NextcloudRetrofitServiceMethod.invoke() at line 124 with the suspend methods in the shown BookmarkService interface. Compare the parameter annotations and coroutine-generated method shape with the Retrofit 2.6.4 dependencies. Done means both suspend calls work without the exception while preserving their query parameters.