Those tanks do have higher failure ratio and 1 of the theory is that if you run it less than a 1/2, the inside sensors might get exposed and fail.
Top off the tank, clear the code and recheck next day.
What scanners do you have?
I would check live data on DEF tank level and Nox sensors performance.

 

I replaced the internals in the fall, Heater failure. The scanner is a Foxwell.
Last week I got the "adblue" msg, and filled it up that afternoon. Started the # of starts countdown, took it to a MB certified Mechanic. He was able to stop the counter, but said the code 204F96 would come back and would need to be addressed by a dealer with "Xentry log on".
Before taking it in, I dropped the tank, looked inside and everything was clean, no "crystallization" etc.

 

How mechanic stop the counter without figuring out what's wrong? What code you had when count started?
I think at this point you are at mercy of dealer. If you'd have to replace a sensor, it will require SCN coding and indies can't do that.
Dealers milk customers on Nox sensors done in pairs, but you can buy it from net dealer and have them install and code it.
If it is DEF in tank unit, you should have warranty?

 

I think at this point you are at mercy of dealer. If you'd have to replace a sensor, it will require SCN coding and indies can't do that.

Independents can do that if they have a valid Xentry installation. I do not work at a dealer and can SCN code a program modules, etc.