There is a problem in MQTT connection.It was randomly disconnected and when we click save button its connected automatically. Let me know what was the problem.Attached screen shots for reference.
Are you using the latest version of MQTT extension which is 2.1.2? If not, you will find this in the Software download page under Release 8.5 -> ThingWorx MQTT Extension.
One issue which I remember is that IsConnected & LastConnection properties were not getting updated and the thing was being shown as disconnected although the actual properties were getting updated from the broker. The next version 2.1.1 and probably this one too had issue with connecting over SSL. So, it is recommended to use 2.1.2.