I just received a Mifi (really 2 but only one with a 4g radio) and I’ve noticed some odd behavior. It’ll stay connected all day long here at home but when I travel with it it frequently seems to stop working. What I think is happenig is that every time it switches to a new cell tower it’s getting confused. The Cellular light continues to blink as if it’s connected and transmitting but that’s it. I don’t know if it’s getting a new IP address and the Mifi isn’t noticing and doing the right thing or something with the actual radio. I haven’t had time to dig into it much but If this is a known issue with a known workaround I’d appreciate some advice. BTW this is on Verizon in the USA.
I see.
I traveled in Europe and it works fine most of the time. Just one time I have this issue.
I don’t have that particular problem with AT&T (yet). I haven’t traveled with a Tmobile SIM in it too much, but when I did, it changed towers fine.
If the signal strength is marginal, it does do strange things sometimes, but not quite like what you are describing.
I drove around southern Europe with mine last summer and noticed it lost connections in some areas quite a bit, even though my phone didn’t.
The light was on but there was nobody home 
I thought that it must have been either the heat of the sun in the car window or buggy hardware/software
I have never seen this behaviour in Northern Europe, even in very remote areas, and so I’m thinking it was just the heat in my case