actually I just made this observation:
- QW787 at Gate 564 at Simwings EGLL (P3Dv5)
- did catering first, then called Fuel truck
- for over 10 minutes, the fuel truck seemed stuck (text said not "on it's way" but stayed at "requested"
- reset GSX and called truck again - it came after about 5 minutes
So there seems to be cases, where the fuel truck just won't start driving.