Same here, this is also kinda similar to this problem with the Gdocs add-on I recently reported: Reloading Gdocs-page after standby?
Also this is sadly one of the biggest downsides of Paperpile, basically its Achilles’ heel.
I also often travel by train and there I’ll have a unreliable connection.
So the reader will switch to offline mode at some point, disabling the annotation features.
And to resume as stated you have to reload the page and it will not have saved the state obviously.
Can’t you just wrap the app in Electron or something, one of your competitors seems to have done just this with their recently released desktop app for offline functionality 