When you open the app all the posts you were viewing before are gone and fresh posts are fetched after waiting depending on your internet speed.
Instead, how about immediately showing posts from the previous app session and fetching new ones in the background. When they are fetched a button “new posts” appears on the top which can be clicked to scroll to the top containing the new posts.
+1 for toggle. In my case:
My internet is slow sometimes. The feed and images take a while to load.
I often forget to read a cool post and switch to another app, restart my phone etc. I don’t even remember what it was to search for it and it’s gone forever.