Flywheel keeps breaking

MAy be too tight of fit of the converter into the snout, a missing or defored dowel pin.

Bring it back to the engine replacement folks.

There is a lot of value in sticking with one shop as in this case. Now there is a finger pointing issue that gives both shops an out. What I don't know, is the definite cause. It needs to be taken apart and analyzed at to why it's happening. I would go back to the original shop that put the motor in and explain the situation. Becareful to not put them on the defensive and don't be accusatory. Ask about the possiblities of why and if the engine company may be able to explain it. I assume this was a remanufactured engine?

See if you can find out what this engine came out of. There should be a paper trail leading back to the original car. I am thinking there may be a difference in the flywheel that isn't compatible with what you now have. See what you can find out, usually there should be a vin number that is obtainable from the used motor's car it came out of. If you can get me that and your vin, I may be able to find out the problem.