ipadOS 14 showing emails unread
It’s not clear which mail client you’re using, but this isn’t a bug with the native app on iOS 14 and just something that happens.
Since you have IMAP, I would delete the account from any device you feel is out of sync. In your case, delete the account(s) from the iPad and then power cycle the iPad.
Add in one account only and see how it reacts. If fine, repeat until you’re happy. If not, there are other more intrusive steps you could take.