Vapor lock is caused by gas boiling in the gas line.
If the pump is at the engine then the line back to the tank is sucking fuel. The suction lowers the atmospheric PSI and lowers the boiling point. Higher altitude lowers boiling point.
In tank pumps help so much because now the fuel is pressurized the entire length of the line which RAISES the boiling point.
Winter gas has a lower vapor/boiling point so if you use it in the summer you are asking for trouble.
It could be Vapor lock or a cracked fuel line.