I'm going through this myself and finally decided after a year of fighting and cleaning out the bins completely a few times and downsizing twice to just bite the bullet and cull the entire colony. (Last time I killed off about 90% and it didn't work.) I'm hoping to find "fresh" adults locally to start back up in the next few weeks. It was not easy making that decision, but knowing that any future roaches born were doomed to die ugly, feeling that I couldn't safely feed them to anything without knowing for sure what was wrong, and not knowing if it could spread to my other species I felt I had no other choice.
On a freshly molted adult that was dead I found what looked to be roundworms. They did not seem like maggots, but looked like some sort of nematode. And my colony has been acting exactly the same as yours - neurological signs, death, and then very quickly being eaten (either by whatever hatched out of them or by the other roaches.) Haven't been getting many nymphs either. I had been thinking it was something mental causing them to attack and eat each other, but the presence of nematodes was the red flag and there was no more waiting.
I will say this - the invert room is a pleasant smelling place for the first time in months! And so far there's no sign of the "infection" having spread. *crossing my fingers*