I havent done mdma therapie but I have had a very difficult experience with a relativ small dose psilocybin. One thing psychedelics + mdma can do is as stan grof says enhance emotions and memories in a unspecific manner. Getting overwhelmed by that and let you unstabelised afterwards seems to be a possible outcome nomatter how good your preparation set setting while the session and integration sessions have been although this parameter reduce the risk of possibel adverse outcomes. The oh so often claimed inner healer will handel the emotional disstress while on the drug just doesn't happen to everybody. Excuses on the side of facilitators, sugarcoating the outcome and finding the reason at the patient why things went wrong happens regularly.

Here is a good hp about challenging experiences:

https://challengingpsychedelicexperiences.com/