Welcome to our forum, @Odin_Nosen. What Android device and OS are you using?
The first suggestion would always be to attempt signing out and back in of your account on the Paperpile app, let sync run and check if the issue persists. If it does — what exactly isn’t being synced? There is a known bug with Samsung and Onyx tablets where annotations don’t save, which will be addressed in the next update of our mobile app. Let us know if that could also be the case for you.