Similar to MCPE-173580 my son hasn't been able to play Minecraft on his iPad for 3 weeks. Minecraft crashes 3-10 seconds after starting. I've re-install the app, wiped his iPad to start from scratch and restored backups. The app crashes keep happening.

However if Minecraft is not signed into my son's Microsoft account, then the app does not crash. My son can play in his world and browse the marketplace, ... But his Microsoft account (and Minecoins!!) is not available. He can't play online. The moment he signs into his Microsoft account, the app starts crashing. Signing out quickly at the start of the app works - the app doesn't crash afterward while signed out.