I don't think it's my rub... I have a theory and that's carryover heat overcooking my flats.
I've vented them for only about a couple of minutes and then foiled + rested for many hours (had to transport them hot).
I'm gonna do the next one as I've done all the previous ones, except vent for 15 minutes and rest for 1-2 hours max. Maybe even keep a thermo in there during resting...