When using the new MQTT websocket capability from firmware 2.4.4 via mqttws31.js it happens that the connection is lost due to an internal error of the websocket library; nevertheless, as the error message states something of "malformed UTF data" this might be checked on the FLM side as well.
See https://github.com/gebhardm/flmlocal for error message sent in the browser console (error occurs on message received).
Note: This is no issue with the updated MQTT broker in firmware v2.4.5++.
A reconnect onConnectionLost (as implemented by JPMens) cures the issue, but does not solve it... console.log still shows the issue even though the script now is not stopped :-/