I tend to agree with you about the charcoal filter. Had this problem on two race cars. Figured out it was from jamming the fuel into the tank before enduros. Topping off the tank to the very top of the fuel filler hose and the associated track g-forces was causing not just vapors, but liquid to get sucked into the charcoal canister, saturating it. Not sure how it is happening on your X, but perhaps that vent valve and the filter together are the issue.

Good luck!

__________________
Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual