It sounds like part of the problem was how the application reacted to the reverted fail over. They had to restart their service to get writes to be accepted, implying some sort of broken caching behavior where it kept trying to send queries to the wrong primary.

It's at least possible that this sort of aborted failover happens a fair amount, but if there's no downtime then users just try again and it succeeds, so they never bother complaining to AWS. Unless AWS is specifically monitoring for it, they might be blind to it happening.