A safe MySQL upgrade that wasn't so safe

That's kinda fun (not in a fun way).

Since the update is done semi-automatically by the means of AWS RDS, does AWS takes any responsibility for that? Unless this use case is warned against in migration notes, I would think they ought to.

I don't understand why this issue only appeared after the upgrade, not immediately after the migration to add the column?

Mixing binlog formats across replicas sounds like user error to me.