Vapor lock issue?

How in the world can an air pocket stop flow when the pump is pushing the fuel; it cannot. Some fuel may flash to a vapor when it enters the filter, but it will move thru the filter and condense on the other side. The fact that the engine runs at all proves this.
The speeding up and slowing down of the engine, is probably a response to an unstable fuel level, proving that vapors are entering the bowl.
Whenever I get a vehicle with a fuel problem like this, the first thing I do is a fuel pump volume test. Next I check the pump for suction. and finally for pressure. and don't forget the mechanical aspect; the pump lever has to go up AND down , forced to do so by the spinning eccentric on the cam. If these are working as designed, the vapor in the filter will sort itself out.