Occasional disconnects with MC7455/EM7455

[maxguru]

Hi,

I'm new to this forum. I was wondering if someone could shed some light on my problem.

I have a Sprint SIM card. I initially bought MOFI4500-4GXeLTE-SIM4-COMBO and tried using it, however, had a strange problem. I understand that it has an internal MC7455 modem. The modem would occasionally disconnect (see screenshot) when on band 41. Band-locking to band 26 would also cause the same problem, except with much less frequency and with occasional hard modem freezes requiring full power cycle (soft reboot doesn't help). I initially thought that maybe I just have a bad unit, so, I tried to replace it, but Mofi Network is a shit company, so, it took months to get the replacement process rolling and I am still waiting...

While I waited for a replacement, I decided to try the following two items,
https://thewirelesshaven.com/shop/pcie-m-2/m-2-ng ... card-slot/
https://www.ebay.com/itm/174083782024

I've set these up with a Raspberry Pi 3 and ROOter firmware (https://www.ofmodemsandmen.com/firmware.html). I followed the following instructions for setting it up,
https://github.com/danielewood/sierra-wireless-modems

To my dismay, I have exactly the same (or even worse) problem with Raspberry Pi 3 + M.2 adapter + EM7455 (occasional disconnects on band 41). Band 26 seems to be stable so far, I need to do more testing. On band 41, modem seems to fully disconnect and the web UI shows that there are no modems connected for maybe a half a minute. Mofi4500 seems to have had the same issue with modem fully disappearing from the system (see attachment).

I checked my mains voltage to see if there is an issue with that, but no, everything seems to be fine. I have the hardware connected to a UPS (https://www.amazon.com/gp/product/B013JHYQNC), so, there shouldn't be any issues with voltage or current.

My question is, what is this thing I am experiencing and how do I fix it?

[JimHelms]

The EM/MC7455 seems to not like Sprint. Some run them without issues, while others experience routine disconnects from the tower, regardless of the device the modem is run in.

[maxguru]

Thanks for the insight. What modems do people recommend for Sprint?

[JimHelms]

Most have gone to using the EM7565 as long as band 41 is available--since it does not have band 25 or 26

[maxguru]

What about other brands? The firmware I am using seems to support multiple options (https://www.ofmodemsandmen.com/modems.html).