Android Work Manager: "Could not instantiate Worker"

This is a known issue with WorkManager 1.0.0-alpha09 that is already marked as fixed for alpha10.

As a workaround, you can add the following lines to your proguard configuration:

-keepclassmembers class * extends androidx.work.Worker {
    public <init>(android.content.Context,androidx.work.WorkerParameters);
}

I had the same issue. The cause of the issue for me was that my Worker class was a nested class. The moment I made it an independent class, it worked.