I've had reports of this before from clients of mine who are users of other Shopify POS apps and now I'm experiencing it as a developer, but it's been difficult for me to reproduce. It seems to happen especially when there's a "cold start" of Shopify POS after it hasn't been used in quite some time - this morning, for example, when I first loaded my embedded app within Android, it took me to some random part of the Shopify Admin (not even the web UI of my own app). I've also experienced it just hanging. On iOS on the other hand, it's pretty rock solid.
I realize this isn't much to go on as I didn't capture the actual logs to figure out what is or isn't firing, but has anyone dealt with this type of flakey behavior before? I'm inclined to put a big disclaimer on my app listing page with caveats for Android Shopify POS users.