MCB board does give the reason for abort

Are you in the states ? I've not heard Americans refer to controllers as MCS before .. That's how we refered to controller in the u.k ..mcs 120 , mcs 220 etc... The reason I ask is the process is different if your using the European controller for example do you have NTSD and ETSD vanes and switches ? On the American controllers if it aborts a learn run it will give you a reason for this in the MCSS logb ( M-2-2-2 ) . Not in the drive .

I'm sure even if your using a controller from Berlin you can still check the M222 log for reasons a learn run is aborted

Am using the controller from Berlin.
You're right the error log is in Motion control board not really the drive.

What did the MCB log say ? I've not worked on European controllers for 9 years , we used the 220 back then for traction . Guess the 321 is similar ..