#Fedilab remembers your position (and updates your Mastodon marker, so you can keep the same position between apps). Of course it has a limit when cache is enabled. If you have an active Home timeline, the app will remember your position but you might end up in a gap where many messages are no longer available on your instance. We introduced background Home retrieval while you don't use the app. It's not perfect but it helps. Otherwise, you can disable cache in settings.