Weird.
It could be gill flukes, in younger fish they'll kill them before they start to display crazy flashing behaviors.
I really don't have any advice, if I were you I'd try to find private breeders whose stock has been isolated and bred from healthy angels.
If that won't work then my only other suggestion would be to run all of the standard rounds you should with wild caught fish...
Formalin dip, metro treatment ect.
Check with simplydiscus.com on proper treatment of wild caught fish, their medication/disease forum is crazy in depth and some of the members are vets that sale medications you can normally only get through a visit to the vet.