I can reproduce this! At least in my case…
So I have a dropdown (ENUM) field and I’ve checked “Allow other values” in the view and entry settings…
When I put in a new value and save the record, BAM! I get the error. I’ll try adding the value via database edit, but it appears there is a bug with this option!
Also discovered a “Reset Changes” in the app menu, the only way to clear the issue on my phone - other than clearing all data for AppSheet.