Trouble with Viper Vortex PST 1x4

I have a Vortex Viper PST 1x4 in a P.E.P.R mount on an AR with an LMT lower, Ranier Arms match upper, Ranier Arms Match 18" barrel, BCM KMR 15 handguard and a Dead Air Brake. Usually this shoots one hole groups at 50 yards (chosen zero) without issue. Started shooting erratic groups and with a bent KMR rail I figured the rail was to blame. Replaced rail today and it did not fix the problem. Normally use Hornady Whitetail in this rig as I use it for Coyote removal operations. Never a problem until recently. Tried every variable and could not get the gun to group or to achieve a solid zero. Final variable tried was to go from 4x to 2x on the scope. Did this and everything went back to normal with Whitetail and Walmart Federal 223. Went back to 4x and could not zero or group and adjustments are way off. After some research on the Vortex website and it stated that problems with zeroing could be due to overtightened mounts.

My question for the group is whether or not anyone else has experienced these issues and why it works at 2x, but not 4x. If overtightening is an issue it seems like it should be an issue at any magnification. Thanks in advance for any knowledge that can be imparted!!

I had a warranty issue with a Vortex scope a few years ago. They replaced the optic without any hassle. Excellent customer service.

I've heard of issues from some 3 gunners with the PEPR mount and return to zero. I have the same scope in an ADM mount and have not had issues. Not sure what would cause the difference in 2x to 4x.

Hey Bowietx.... Just wondering, What has happened so far? Have you shipped it back?