GrapheneOS I never had any issues with rotating the screen. But many apps lose any half-typed message that has not yet been sent or posted if unloaded. Many others lose their scroll position. Some even jump back to their home screen or default dashboard. Vanadium is one example of an app that is handling this especially poorly. But every single end-to-end encrypted chat app I have tried also cannot handle being unloaded without losing my half-typed message.
I understand apps are supposed to be able to handle being unloaded gracefully, without losing any state, but the truth is that this seem to rarely be handled well. Many apps cannot be put in restricted battery usage because of this.