Equipment missing from inventory

I have a GX-440 that has been added to the account and it will go through the registration and import all of the modem information, but if I login a few hours later the device is missing again. This is only happening with one device and is one of the original devices on the account. We used the trial initially and when we added more devices purchased the management services for all of current and new equipment. ANY suggestions as to why this is happening?

Can you do Factory reset and re-enter the module and check the issue is still there? Also ensure they are on the latest firmware 4.3.6.
Then of course confirm the Server URL is correct.