D motor mount damage - not really sure what happened here

This new 24mm D and E capable motor mount failed after nine flights.  You might see the motor tube burned completely away about an inch up.  The thrust ring and forward centering ring is still there.  The last three or four D12 engines blew past the motor clip and ejected itself as well as the parachtues. After I bent the clip a little tighter to prevent that from happening again, the second last one ejected itself anyway and took the clip with it!  The last flight with a D12 was friction fit, and it also ejected, burning the tube wide open inside.  Several of these flights used a C6 in an 18-24mm adaptor, and one or two used a C11 motor, but I did not ever use an E sized motor yet. All flights used an Estes spacer to allow 70mm length motors to fit properly in this 95mm motor tube.  There were no motor CATOs, all flights flew as expected, delayed and ejected at altitude.

Was the motor tube just too weak and thin?  This model has a 2-plate ejection baffle. Perhaps the ejection pressure was too high from a baffle that was too restrictive?  It might have caused hot gas to blow back around the motor casing and eventually weaken and destroy it. That seems to be the only possible cause of failure, and it would explain why this model kept ejecting D12 casings.  I really have no concrete answer to this, has it happened to anybody else and did they find out why?