Maybe I should have characterized it differently than, "the material hardens when vaped." More accurate would be, "unspent vapor in the chamber condenses and becomes sticky then solidifies, effectively adhering the mouthpiece screens' flange to the top rim (the end) of the body's chamber." I think this is the most likely cause of the 'loose screen syndrome'. (When you try to unscrew the mp, the screen stays put and becomes un-threaded from mp).
So, extra drawing after shut-off is valuable for clearing the chamber of said vapor. Emptying the chamber while still warm helps prevent said sticking, or re-warming if it's been allowed to cool may help loosen said adhesion and prevent the screen from loosening.
I had become re-aquainted with standard mouthpiece for the past couple of months, native use. But recently I removed screen and internals from one AFTER 24 hr iso soak, rinse was still dirty, another 24 hrs then rinse, then inspect and that little plastic thingy attached to the screen was still dirty, as were parts of the metal inner funnel. It's too many pieces for my liking, so I'm back to PFE -- this time with a SS 510 drip tip that does an amazing job at cooling both vapor and the surface touched by the lips.