Two causes of this and you might have both.
1) Tank not level. If the tank is not level, water will start coming out the overflow vent and stop filling long before the tank is full.
2) The vent line is kinked or full of water causing the water to back up in the filler tube under pressure.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW