I suspect, after many problems over several years, that my Pepwave SURF SOHO MK3 has a hardware problem and will never actually behave well. I’m still working with it, and I might get into the 8.1 firmware beta, but I remember that at the very beginning it had problems with the power adapter, which is why I do not unplug the power adapter at the unit, but rather at the surge suppressor (where the “block” is on the cord).
So, I went looking for a replacement and I found a couple entries on amazon.com for the “SUS-SOHO-T”:
Sorry for the delay in responding. The seller of the model I bought in 2017 was Amazon.com Services LLC. The attached screenshot shows the info that Amazon has about my order. In the screenshot the link goes to the following entry: