Under your account settings do you have "show read posts" disabled?

Community of the Android app Boost for Lemmy

Under your account settings do you have "show read posts" disabled?

This was it, thank you! I was looking under general and appearance settings, did not think to check account settings.
This would be my best guess.
Do. you have "hide on read" or a similar toggled in settings?
I don't have boost anymore but this sounds like it's automatically hiding posts that are marked as read which can happen when you interact with the post by commenting or even upvoting in some cases.