Hi,
After an Oreo update in September my Nexus 6p has no LTE only 3G, I tried provisioning using *#*#4636#*#* and noticed that while setting for LTE it stays on that setting for 5 seconds then changes over to EVDO/3G as default.
I've gone in the Verizon store and changed sim cards and no change. This is consistent with everywhere I go, in state and out of state.