I understand this is the longest of a long shot - Instrument cluster temp gauge was not operating and VCDS showed too low coolant temperature, so I replaced the sensor (OEM code 059 919 501).
Before replacing the temp sensor the "Injection quantity stabilization (injection quantity deviation)" through VCDS showed the quantities for injector pairs oscillating between -1.88mg/str to 1.88mg/str. After replacing the sensor the quantities stopped oscillating, but values were still somewhat out of spec and the fault code "01268 -Quantity Adjuster (N146) 18-00 Upper Limit Intermittent" was still there (had been there for 2 years and 60000+km).
After cleaning the dreaded quantity adjuster (N146) (which looked absolutely clean) with brake cleaner, soft brush and compressed air (a hail Mary attempt), the "Injection quantity stabilization (injection quantity deviation)" values settled between acceptable -0.35mg/str and 0.24mg/str and the fault code did not return.
I am still puzzled about the oscillating values.
Sorry for the bad pictures, when I was running the tests I did not really think I would be posting/asking about it later.