That is a sabot failure for sure. Why?...I dont know without more info. I had the same issue with the Harvester 40x50 CRs and a few bullets if i tried to drive them a little hard (110gr BH209). Many people feel that the Harvesters are tougher than the MMPs but this one seems to be a bit weaker or i got some bad ones.
I didnt get to finish my testing of the MMP 40x50 vs the Harvester before the hunting season so im still not sure.
T/C uses a MMP 40x50 sabot (IIRC) but it may be a bit different than the ones you can get directly from MMP. My best guess is you got a bad batch of sabots or the bullets are slightly different. Maybe they were slightly smaller OD or the base is different?
More load details and shooting conditions would be a big help.