I have Corsair AX860's running all of my S3's.  They have a "hybrid/normal" switch.  When I flipped that switch to "hybrid" on a couple of my PSU's, I had one board on several rigs stop working.  My hashing power on each of those rigs cut in half.  However, it worked fine when I turned off the power to the PSU and turned it back on.  They would work fine for several hours.  Then all of a sudden I get an alarm from the pool saying hash is down.  I would look at the rig setting off the alarm, only to see the hashing rate was half of what it should be.  It ended up being the "hybrid/normal" switch.  When I flipped the switch to "normal," I have not had a problem ever since.

With that said, "Hybrid" probably limits the amount of power given to the rig once the PSU reaches a certain temperature.  Hybrid makes the fan on the PSU turn at less RPM's.  So, if you do not have Corsair's with a "hybrid/normal" switch, it may be your PSU is not sufficient at providing the power needed to the rig(s).

Still pay attention to Dogie.  He knows what he's talking about.