Hi Christian.
Whatever you did made it possible for me to chamfer those holes, so thank you for looking into this for me.
It still leaves a mystery though, as the holes were created from circles generated by MoI.
I positioned the first circle at 12 O'Clock on the front face and Circular Arrayed the other 5. I then did a Boolean Merge to cut the holes from those 6 circles.

I just tried remaking the solid from the Revolve curves and then using 6 fresh circles from an Array. The result is still the same for me. :-(


Thanks again.
Martin.