When this issue occurs on plex Web, The android and IOS are affected but not all the times. I’ve noticed sometimes it works and sometimes it does not and on those occasions the watch together sessions is not active, it just gives a message saying your libraries are empty or unable to load.
Yes, I’ve reproduced the error using incognito. I would rather not reproduce the error again because I’m currently actively using plex. But I can clarify it also occurs in incognito.