I had this issue. It was a while ago and I think this was the cause, but if it's not, it's still something to be aware of.
If you're developing on Windows, filenames format are not as much as a concern as they are for Android. Windows doesn't care about case or underscores.
I am using a download graphics pack and the filenames are full of underscores. This (I think) was causing the issue. I have to rename all of my files, to remove the underscore (I use a bulk rename utility).
Make sure the case of your files match as well. Godot should give your warnings about that.
If it's not that, try remote debugging?