We are seeing these same issues with Jabber version 11.5.1 Build 29337 as well. Not sure how much I can change since I'm an end user, on this system, but I can make changes on the client side. Suggestions on things to try short of having both clients restart (which does fix the problem) requested.
We also see various "company policy prevents" type messages. Usually its just from one person to specific others; some chats can be initiated in those cases. When I see this chat, I can't reach anyone. However people can invite me into existing chats, and can chat with me.
