*** Solved: it was pointed out there is a Lemmy setting that enables showing read posts, rather than a Sync setting.

At some point I think I enabled a setting to hide read posts automatically, but now I can't seem to find a way to stop this behavior. There is also no method to unhide posts. So now once I've read a post, after I refresh it is gone forever in the app.

Tried resetting all settings back to default and erased user data in android but it seems stuck, maybe to my user account?