I have had a chance to make a test on desktop beta on Mac, and I observed the same issue. And indeed, all of the cards that are reappearing are learning card with inter-day spacing, around 2-5 days. All of them are also cards that have siblings that were also learning cards. I previously was not seeing this because my study circumstances were different: I was not adding new cards to this deck, but I was adding cards to other decks where there are no siblings, only one card per note.
You can test for yourself if you like. It is the “Greek” deck (the parent deck). I studied today but did not sync, so you can test my study session. I made a video demonstration on the latest desktop beta of my steps to see the problem:
https://u.pcloud.link/publink/show?code=XZjWjaXZpH3z8EAwYJScASe1yEW1y07K3ymk