EDIT: FIXED - Thanks to a helpful Discord user, it turns out this was a setting on Lemmy not on Sync. On lemmy.world settings I had 'show read posts' unchecked. I presume that's default unless I ticked it by accident. Whoops. I'll leave this post up incase it helps anyone else though.
If I read a post, it gets hidden (after a page refresh)
I can't find any way to disable that setting and I really hate it, because I like to revisit threads to check comments on occasion. Does anyone know how to do this?
Thank you for the suggestion! Weirdly, even with that disabled, they still dissapear after I have clicked into them. Although the app no longer marks them as read with a different colour, they still vanish and never reappear after a refresh or app restart.
I'm having the opposite issue; my read posts have to be manually hidden, and then pop back into view when I reopen the app!
ETA: another comment in another post helped me resolve this. You need to login to the website of your instance and update your settings to uncheck "show read posts".
Connect was hiding them in-app, and I'm sure LJ will do the same soon, but for anyone looking for a fix now - that will do it!