Its a message from that the connection to the server has been lost for live functionality. Notifications, user presence, typing indicators, new reply messages, etc. all use this connection to work. I am not sure what version of 11 your are on, but there have been some updates to show the message less frequently as the disconnects are usually brief and cause no visible issues to the end user.
Its a message from application server, when any changes like adding / replacing binaries in the application hosted server, this message will be appeared. it will be reconnected in few seconds automatically.
Make sure you're updated to the latest available hotfix. If you are still seeing these messages a lot there may be some connectivity issues in the environment - things like vpn, load balancers, server slowness, etc.
Are you experiencing other slowness or loss of functionality or is it mainly that the message is intrusive?
