Nox conversion low/def quality

2015 cascadia evo in shop for spn 3364 active. Had a spn 4364 code a few months back but went inactive same day. This def quality code came up two months ago, also went inactive same day and then again today. Checked into shop to diagnose since repeatedly came back but want to have some knowledge on this before I just ok repairs. I know the end all be all could be box 1 fail but since codes go inactive, wouldn't that be unlikely? I would think the perimeters for the fault wouldn't return to normal if box 1 was failed. Would a failing Nox sensor cause either of those codes despite not having a Nox sensor code? I asked the shop to start with the doser, def filter, etc and check for buildup since that too makes sense. I guess what I'm asking is, how common is the Nox or doser the problem vs a box 1 fail? I tend to panic into thinking worst case scenario.

 

Should note it's a Dd15

 

Funny you say that because we've been having some issues with the Snoqualmie pass de-icer eating away at wires. Brake lights especially.

 

Update: It did a successful regen but at 81% efficiency which I guess is above normal but under the 85% threshold. Nox sensors were both in parameter. No active codes, no build up of def on inlet. No accumulation of def in the box. Going to drive it and see if problem persists. I'll update this thread is something does happen.