Ok so you have no CEL, but did you scan the system for codes with a bmw specific scanner? Not a generic scanner mind you, you’ll need one specifically designed for BMW. I’d be willing to bet there’s a code or 2 stored in there. If the system can’t vent for you to fill your gas, it can’t vent to run the evap test.

__________________
Current vehicles
2001 325XI
2006 X5 3.0
2004 X5 3.0