I tested on a wide range of devices, from android 4 to 8 and low to mid-high hardware specs.
I got the same results, specially very low framerate when compared to builds with the older tools. I got no actual crash or frozen status.
Trying to find problematic elements by disabling things and features isolatedly yielded no results.
I have returned to the flixel 4.3 environment, but it seems Google Play will not accept android-19 builds from August. Nice situation!
I'll keep investigating (after the game is published!)