LAX 20 Dropping Connection

I am having a strange issue with my LAX 20 router and wondering if anyone might have some insight. This router is installed in a remote location with power and a reliable AT&T cellular signal. It works fine and reliably when we are there. The issue is that it after we leave, the router drops its connection and cannot be accessed. It is reported as offline with the Nighthawk app. The other day, a neighbor came by our cabin and the router popped up and was online while he was there. He was outside, never came in, and did not touch anything. Shortly after he left, the router dropped out again. It has been offline ever since. This has happened more than once. The timing is startling. The router loses connection a few minutes after someone leaves and only comes back when someone returns.

We are visiting in a couple of weeks and I a perplexed as to what to do.