Cm 12.1 snapshot issues

I helped my dad get his dlx running cm12.1 in the summer and it's been fine up until recently. He's been updating nightly builds once a week and recently noticed the screen blanking out on him. I helped him flash the 12.1 snapshot build, and factory reset his device, but not LTE seems to be broken. Text messaging works, calls are only successfully if we change the mobile network mode to something other than LTE, and mobile data is non existant.

Is there a specific radio/baseband we should flash or perhaps some configuration to double check that can fix this? I'm not a Verizon user so I'm hoping some of you in the community can lend a hand!