This is a mind bender,

This is a mind bender, While doing a shoot using monolights connected to a Nikon D1x I encountered exposure problems. After the lights were metered for the best exposure, I started shooting. The first ten or so shots were fine, and all of a sudden the next ten shots looked like they were 8 stops over, and then it went to looking ok. The first thing I did was switch monolights thinking there was a problem with the flash, this did not resolve the issue. Next I switched camera bodies, still the intermittent overexposure persist. And the 1-800 to Nikon tech support rendered no soloutions either.
Can one of you Brainiac's solve this puzzle. One other thing, when I switched strobes I also changed sync cords.
I'm open to any wisdom you may share in this annoying problem

Thanx in advance