Yeah, I had a similar problem (well, my app doesn't freezed, but crashes).
I don't know how to debug from PC (like being able to see in what line of code the error is) but you can use print() function to see what your program is doing. It is suppose to print the text in the Output window in the Godot Editor.
I have to recommend to you to update you Android system, that is what fixed my problem. I just realized that my app worked without problem on other smartphone, and in the end it was that my Android version was outdated.
Another point is to use the program monitor in the Android Sdk (in my computer with Linux is inside /home/Android/Sdk/tools/monitor), that lets you to receive a lot of messages and info about normal and abnormal program functioning in your smartphone. You have to filter all the messages by setting a new filter "by Application Name: godotengine" to be able to see the needle in the haystack.
I hope something of this can help you. Good luck.
EDIT: For example, I just solved a problem I had right now similar to yours (with freezing splash screen) using the monitor. In it, I saw lots of error messages, but some were related to errors loading resources. In the end what happened is that I had a path to a resource in a preload like "/dart/dart.tscn", and it worked fine in PC but not in Android, where it must be "res://dart/dart.tscn". Without the monitor I never would found this error.