P-rod owners, did you experience grip movement??

So, just got my first p-rod thru Amazon.

Out of the box I would say it has a really nice trigger.

How ever I was very surprised to feel the pistol grip very minutely slide/slip/move every 15 shots or so.

I tightened both sides a little. Gotta say was already fairly tight. Don't want to snap the plastic tightening too much.

A known issue?

Thanks for your response