Retracing my steps, when it happened the 1st time I actually hadn't yet connected the 3rd amp in the chain however I had connected the trigger out cable from the 2nd amp so it wasn't actually connected to anything on the other end i.e. the 3rd amp. So I thought that's what the problem was and I immediately shut everything down, connected the trigger cable to the 3rd amp and it happened again.
I then looked very carefully at the wires to make sure neither of the 2 input wires going to each amp were touching each other, did the same for the output wires then made sure the input wires weren't touching the output wires. All was good, I turned everything on and it happened again. So I just set them all to manual and went on about my business

After reading the above comment instead of turning the entire system on I decided to just experiment with the amps. Turning on the Lexicon triggered the 4 which then triggered the 1st 7 then the 2nd 7 came on. OK weird, it works now however I didn't mess around with the wires so what gives. I then shut the Lexicon off and then turned on the entire system and dang it, the problem came back. So what 's different? Well the Lexicon has 3 triggers, one power on trigger which is what is connected to my 4 and it also has two programmable triggers which I use to turn my 28's on in separate 10 second delays.
So getting back to the above comment I think what might be happening is that once all triggers are in play this is to much for the Lexicon to supply and it's the power trigger that starts acting up. The two 28's aren't exhibiting this issue so their triggers seem to be ok.
Do you think if I just move one amp off the power on trigger and chain it to either of the 28's the problem might go away? Or because I'm still using the same number of amps simply moving where one gets triggered from makes no difference because the overall voltage remains the same?