2017 Silverado, L5P w/81K miles. Starting to get code P20EE which suggests a "low catalyst efficiency". I can clear the code with my Edge and drive for a certain number of miles without the code reappearing- but, it eventually returns. I've seen some owners claim the #2 NOx sensor or the DEF injector may be the culprit.

Question: is there a problem driving this thing in the near term without major problems? I can force a "mobile regen" via my Edge, so I believe my DPF is being serviced. Maybe a flakey NOx sensor? A carboned/dirty DEF injector nozzle?

Where on the exhaust stream are these injectors and sensors physically mounted (any pics/diagrams) available? Any thoughts or suggestions?
Thanks!