I wouldnt say they come loose more often on our chassis than other stocks. Over the last 2 years I have only talked to 2 customers that have had issues with action screws coming loose. They were both pretty light 300 PRCs. We had them both put a little bit of white lithium grease on the action screw and torque them again then we didn't hear back. The action screws that we use are a mass produced screw so what we believe happened is the screws were on the higher end of tolerance and the action is on the lower end causing some binding between the screw and action before the screw is truly torqued to 65 inch lbs.
Another possible issue is guys not keeping up on routine maintenance and checking to make sure their screws are tight. Personally before I leave for a hunt or match, I check every screw to make sure it is tight and not going to cause any trouble. I haven't ever had a screw come loose on me while shooting my rifle. We see it at matches with both chassis and stocks where guys have action screws come loose after flying or driving to matches. Even in a good pelican case the rifles go through a lot of vibrations while traveling in trucks, planes, or RZRs.