So since lowering KRKTE did not solve the issue at all, can you give me any pointers what to do next?

rka_w and rka2_w need to be added to the *.ecu and *.cfg file. I'm 99% sure of the RAM address.

Long term fuel trims:

Idle
rka2_w 0x3823E6, 2, 0x0000, {%} , 1, 0, 0.046875, 0, {additive adaptive correction of the relative fuel amount Bank 2}
rka_w 0x3823E4, 2, 0x0000, {%} , 1, 0, 0.046875, 0, {additive adaptive correction of the relative fuel amount}

Part throttle
fra2_w ;{AdaptationPartialBank2} ; {multiplikative Gemischkorrektur der Gemischadaption (Word) Bank 2}
fra_w ;{AdaptationPartial} ; {multiplikative Gemischkorrektur der Gemischadaption (Word)}

Short Term FT's:
fr2_w
fr_w

Edit: The above information is for ME7.1 M box.

And here is an me7l log file of a 100km drive which shows that my bank2 is often way richer than bank1 but then they are equal.