With the update to B4A 13 Beta, the overall APK size increazed and the first compile in debug mode slowed down. Because of that, the first debug run takes quite some time and when the app is finally installed on the device, the debugger does not connect anymore, resulting in this message which times out eventually:
The debug toolbar then looks like that (notice the stop button is not active anymore):
When I click the debug button again, everything is a bit faster and the debugger attaches correctly. But that means, I have to start the debug session two times. I'm not using the legacy debugger and I've increased the process timeout to 80 seconds, but I don't think this has an influence on the debugger attaching. The debug itself does not timeout, it's just the debugger that's not connecting.
I had the problem in the past as well, but not as often. Now with Beta 13 it is everytime on a fresh debug session.