I had similar issues with the WP7702 on an AT&T LTE-M1 connection. Crash & reboot at random intervals from 60seconds through 30-40minutes. After 4 weeks of debug, analysis & rebuilding of everything multiple times I banged on SW and they finally acknowledged an Modem Firmware instability issue that they’re know about and are working on. This was months ago and no resolution nor indication of one. I was forced to move on to another platform. Here is the link to this issue: Intermittent WP7700 module Failure: [Fatal error on the modem]
Good luck!
Mike