Theres 2 things.
An unskilled professional. That's about the person more than therapy.
2nd thing is whrn the defences people have used to keep all the "bad" in check begin to not work any more. That can feel pretty bad. But to be honest. If my defences were still keeping the bad in check then I wouldn't have been in therapy.
Whrn a alcoholic drinks and it no longer blocks things out. Thst already a pretty bad place to be.
It takes, time to work through the bad. It takes courage.
Leaving because things get a bit tough will leave someone in limbo and yes a sense of therapy having made them worse.
But as I say you can't confuse able therapist with quacks.