You're not alone with this issue. I work in an office in Mays Landing, NJ and Verizon LTE signal is relatively weak indoors here since we're in a semi-rural area surrounded by forest.
I work in the IT department at my company. We have 2 Verizon 4G LTE Network Extenders (1st gen) set up on both ends of our office set to their lowest power level to prevent the signal bleeding too far outside into the parking lot. Over the past year, there have been ZERO issues.
A few weeks ago, both extenders updated their firmware to "Software Version : 3.1.1.00"
Ever since then, BOTH of them intermittently stop working with the "MME Communications Error". The only way to fix this is to unplug and plug back in the extender. Furthermore, I can actually trigger the issue. The extender can be up and running, if I run the OOKLA Speedtest app, after the results come in, the extender crashes with the same error.
I repeat, this was NOT an issue before the 3.1.1.00 firmware update. This is definitely an issue caused by Verizon's software and must be fixed. I doubt it is a coincidence that not one, but TWO extenders are exhibiting the exact same issue and have become completely unreliable.