I’m sorry! The SIM800 definitely has quirks, but it’s better than this. We have had better luck with the Mayfly and Digi LTE XBee3’s than you have had with the UBee, but I’ve spent a lot of time tweaking things to figure out what works.
It’s funny, we were on a phone call at one point with a group at Oregon State that was just beginning to look into adding cellular connectivity via a breakout of the SARA R410M. The guy working on it said something to the effect of “we haven’t had any problems with it so far” to which my response was “then you haven’t been working with it long enough.”