Since update I eventually get this picture:
So it sets/shows a backlog although there is none. Just a glitch, but should be fixed anyway.
Version 2.1.63 (f356f177)
Python 3.9.15 Qt 6.5.0 PyQt 6.5.0
At the beginning of time, it seems to show some card, hardly visible.
Not really. When hovering I get

Only the “ago” part changes. Others2 lines stay the same.
Please let me know the deck you’re having trouble with, so I can try to reproduce it with your AnkiWeb collection.
It’s WaniKani. The situation does not happen all time, but it’s been more than once.
This is a bug in the stats. A fix will be in the next update; for now you can ignore it, or empty your filtered decks to make it go away.
Thanks! As said I look at it as a glitch which does not really harm…