If you are in chat channels with 3k+ people then a lot of CPU is used for maintaining the user lists even when you are not looking at the user lists.
I did sort of a bandaid by making that list-maintenance more efficient, but it might be better to completely remove the need to sort the lists at all. In my quick explorations it seemed like maybe list sorting could be moved to the Chat view instead of the chat manager, but I didn’t go too far down that road. Lemme know if I can help with anything!