K9 is still pushing old emails to the top

I’m using K9 since years now,
and it often shows old emails on top, marked as read and the timecode is always the same for all emails, but these emails arrived months ago, some of them last year.
Its always the emails from one email address, and only the old emails from this sender show up on top…

What does the Date header of such a message look like? You can get the raw value by selecting “Show headers” from the menu when viewing the message.

Hello, I already deleted the old emails because it was very annoying, some of them I didn’t even see in my thunderbird anymore, they were only available in my GMX email page

but I think this info could help:

I moved these emails on my PC via Thunderbird from my GMX account to the Gmail account, and later back

Oh, that explains it. This is a known issue: