No fuel flow?

I have an issue where after driving a while, the engine will cut out due to fuel starvation. Flowmeter says there's no flow, and nothing coming out in the carb. Took the gas cap off and it hissed pretty violently. Added some gas because we weren't sure that the fuel gauge was working, and maybe it ran out, and it started working again.

My theory is that it may be a plugged vent line creating back-suction in the tank so it can't travel down the fuel lines, and that removing the cap to purge the vacuum was what fixed it.

My friend is thinking it ran out of fuel and that the fuel meter isn't working right, and that adding the gas is what fixed it.

My question is, which is more likely, and would a blocked vent line or lack of vent line create a condition where there's enough vacuum in the tank to keep it from being pulled through the lines by the pump? Or maybe both of us are wrong and it's something else entirely, and there's other areas I need to investigate.