ZTE Velocity Hotspot shutting down

This seems to be a common problem (links below)  that I am experiencing, but what I've found just says to come here for advice.

So here I am.

They also say to send a PM here with personal details, but I don't see how to do that.

The problem is that the ZTE Velocity Hotspot just stops, shuts down, after a while.

• Part of the problem was that WiFi sleep was turned on, but  we've gotten past that. It is continuously on.

• One AT&T rep suggested that the battery is sensitive to overcharging, but I've been on the provided plugin transformer so that should not apply and the unit is fully charged (green LED).

• I am on a boat in a rather dodgy area, so reception is not all that great all the time. Does the ZTE shutdown if it loses the signal, and if so, how to turn that "feature" off? I still want to use the WiFi for local network usage.

• It turns out this is a common problem. The following posts describe my situation exactly:
https://forums.att.com/t5/Other-Phones-Devices/wifi-mobile-hotspot-keeps-shutting-down-and-restarting/td-p/5178379
https://forums.att.com/t5/Other-Phones-Devices/ZTE-Hotspot-Restarting/td-p/5178963
First let’s try a soft reset. To do this hold the power button until the device powers off, wait about 30 seconds then power it back on.
If the issue persists next is a master reset. This will erase any personal data. Please visit our Device Supportpage.
Make sure your device is selected, and then go Tutorials > Troubleshooting > Reset device. This will have a step-by-step and a video.
Lastly if the device is still with in the 14 day BRE period you can take it back to point of sale to exchange.
To find out more about our Return Policy, please check out this helpful webpage.

We have done all of these, including the last, twice, to replace the unit. So something else is amiss.

If these steps did not correct it; we will need to investigate the cause and provide options. Please send a private message to @ATTCares, and include your account and contact information, a good contact number, and the best date/time to reach you, including your time zone.

I'll be glad to do that, but don't see an option here for doing so. Do you mean to send a text? This is a bit long for a text, so perhaps there is an incident number I can cite while sending the personal data?

Obviously not a simple problem. Thank you for your service.

Best regards.