having same issue with low difficulty on a few workers that are hashing over 4k. Worst part is that worker gets banned even though the server is still accepting work for suprnova.
On top of that, when the worker gets banned, it doesn't send an email of an idle worker. Tested by taking a worker not banned offline and still no email 1 hour later. Block emails come in just fine.
Low difficulty means invalid work, that can happen with some overclocking settings.
Banning should not happen at all unless you send ONLY invalid shares for a certain amount of time.
I'll check banning again though.