I’m not sure if you ever come across issues when there are more than one users editing the page builder as Shared builders: even when one user quits the page builders, it’s frozen and keep showing “being editing by other user”. We tried to login / logout / restart the laptops on both sides but it still the same.
I’ve experienced the same issue; sometimes the only way to cure this is to remove the shared builder and then re-add them, which is highly inconvenient.
That said there seem to have been some improvements in this area in the last couple of weeks, so hopefully you’re seeing better results now.