Hello there. 

Welcome to the Three Community. 

Since the device is intermittently reporting the SIM is invalid, it sounds like there's an issue with the SIM, or the SIM card reader. You could try to determine which one it is by testing the SIM in a phone for a while, and testing another SIM in the hub for a while, then checking to see where the issue shows up again. 

It might be that one of those things need checked out or replaced, and if that's the case, you can speak to the Support Team to find out what needs to be done. 

Pete.