Getting this same issue. I signed up for Realms, created Live accounts, and initially, my child's live account wasn't configured for online play. The game told me as such. Once I figured that out and thought I had it configured correctly, that's when the crashes started. Both on my account on my phone and the child's iPad, presumably because we're correctly configured at this point? I caught this before it crashed. Usually it crashes as the white Mojang splash screen. I can confirm the offline behavior you mention is the same, too. Locks up after 5 or so seconds of trying to sign into Live.
[media]I created a thread on the support forums for this, hoping someone finds a work around...
Present in 1.16.210. I harvest the eggs and when I want some turtles, I plant them and just hang out, feeding the babies to adulthood with seagrass. Walk away or do anything else and they're gone. Adults persist.