iOS14 inbox emails disappear after some time

Hi,

I’ve recently upgraded to iPhone 12 Pro Max running iOS 14.4. The worst problem with the OS is that some inbox emails disappear after a day or two. Not all of them. Only some emails. Sometimes even unread ones. Happens to 2 imap accounts from 2 different providers. Restarting the iPhone did not help, same with deleting and adding the accounts again. The emails are still present on the serves as they are accessible from the web. They only come back when I move them to a different folder on the web and then back to inbox. Then they reappear but sometimes disappear again after some time. It’s happening to 20-30% of mails and also seems to be related to inbox only.

Thanks