I had the same issue with my Apollo !
Was the Mach131's socket : http://leblogdecosmos.blogspot.fr/2011/09/apollo-support.html
The socket appears to have bulged outwards. How did that happen?
@AmiBoy
Check there isn't some play between the accelerator's slot and the 1200/Mediator edge connecter as I described on Amigaworld.
