Just sent a support ticket to ST.
Since I came back from work, my hub goes on and off non-stop
The light change from blue to green. It works for a couple of minute then goes off
I tried to restart the hub, the modem, the router and update my smartapps without success
Can you clarify if on and off refers to powering on and off or if you mean online and offline?
I believe @johnconstantelo sees your statement as referring to a power issue (which it could be). But I believe you are going online/offline since you mentioned the led light changes between blue and green. If that is the case, try swapping out the Ethernet cable and plugging into a different port on your switch/router (that is if you are using Ethernet and not wifi)