LTE5366 keeps dropping carrier-side

I’m in the UK. 

A few days ago I purchased an LTE5366.  I’m using it with an EE 4G SIM.  It’s set to IP Passthrough, to a specific MAC address.  It’s directly connected to a Unifi USG 3.  In turn, this is connected to a Wifi and wired network.

The problem I have is that, intermittently and somewhat randomly,  the network-side connection from the LT5366 drops.  I have to power-cycle the product to restore the connection.  It does not seem to re-establish on its own.  It has run for more than 24 hours without dropping.  At the time of writing, it’s dropped three times in the last half hour.

I have a good signal here (around 30Mbs download) and three other devices in the house, two 'phones and another 4G router) which are working perfectly and not suffering from this problem, which strongly suggests it’s not a carrier problem. 

Can anyone advise what I need to do in order to resolve this?

Thank you. 

I should probably add that I'm reasonably IT-literate and capable but I'm also a biologist so best not to assume I've done or tried anything which experts would assume is obvious....

#LTE_Dec_2018