Okay! That was indeed a great catch by @Gzuuus . The issue was that before, new users joining a group with a long history were attempting to catch up on all the group’s previous messages.... This was incorrect because, due to MLS secrecy, all messages prior to the user’s joining are undecryptable for them, so it was unnecessarily fetching an entire message history, which created a significant load on the network (since the payload can be massive for groups with long histories). This was also wasteful. Now, this has been fixed: new users joining a group only fetch from the epoch at which they joined, which is the point from which they can decrypt messages. I’ve updated the coordinator reference implementation, as well as the web and CLI clients. As a side effect, I’ve also enhanced the group info page to include more details about the group’s state and other relevant information. From now on, new users should be able to join old groups without any issues! Thanks for your patience. We’ll continue working to improve the experience as much as possible :)