This message is shown on the small screen on the 4G LTE Network Extender itself. The exact message is:

Servicio interrumpido

MME Communication Failure

As said before, this is affecting 2 network extenders which were bought together about a year ago. They both worked flawlessly for months on end until they were updated to Software Version 3.1.1.00 as shown on the web interface.

Ever since then, every single day, one or both of them will go offline with that error. It seems to happen more often if we have a big meeting with many more people than usual in the office. Appears the Extenders are no longer "resilient" to being run at full capacity. We usually have about 15 - 25 people in our office at a given time. Everybody in our office has a Verizon phone through the company. Looking through the capacity logs, on most days, both extenders are not running beyond the threshold.

The only thing that fixes this issue is to power cycle the extender.