I previously installed lineage OS via and was having trouble getting my Jelly Star to connect to anything but the Edge network with Mint Mobile. I think this probably had something to do with an update that Unihertz pushed out that I didn't have properly installed.
I found this crazy random post and it magically is allowing me to force connect to LTE. I had to dial *#*#4636#*#* and I set my phone's network to LTE only.