Ok, I loaded the scene you posted over on ProSoundWeb. This shows DCA assignments and it also shows your feedback issue. Channels 23/24 are sending to Subgroups 15/16 via it's channel sends while at the same time they are being fed by subgroups 15/16..... Turn off in Channel 23/24 the Sub Group send to subgroups 15/16. I thought you said there were no sends to those Buses when we talked before?
Doug
:edit for clarity: