It deletes the app data after certain time.. I’d say 15 mins.
I think it does this so you can resolve app glitches without having to reload your user data which could be game progress, app sign-on, etc.
I’ve fixed my YouTube app several times by deleting it and quickly redownloading it without having to re-authenticate.
Offload app selection is under General then iPhone Storage once the app is selected from that list