After updating Anki to 23.12.1, I suddenly have 2 phantom cards buried deep in my backlog. The issue is present on both the desktop and iOS clients, both after recently updating. I don’t know what version I was on prior, but it was at least 2.1.66 as I did a clean install of Windows back in October.
If I search for them using is:due, prop:due<=-1, etc. they don’t show up. For what it is worth, the cards are positioned around when I started using Anki.
Other than updating, I recently created a filter deck which suspiciously also has 2 cards. I have it set to only contain is:new cards, and they were new when added, but I have reviewed them so they should be in the “learning phase.” I’m not sure if them still being in the filter deck is expected or potentially related.