YSK there is a setting in your Lemmy profile to hide posts that you've seen. Upvoting counts as interacting with that post and will hide it after refresh.
Also, if this selected, it will hide any posts you make. I have been saving the posts I make as a favorite until Lemmy fixes this.
Yes. It affected every app that I used so far. The only one I'm not sure is connect for lemmy (android), because it has its own hide read posts settings.