Two points...first, do you know what the voltage was from your USB port? Many USB ports do not put out 5v/1a, thereby, not providing enough power for vapor generation. This is one reason some forum members have purchased USB battery packs like the Kensington Portable Power Supply ti insure top-notch pass-through operation.
Second, your pass-through has to let air in for the pressure switch to activate. You might want to search for a USB pass-through for the penstyle that has a manual switch. This is really the way to go, period. The manual switch eliminates auto cut-off times programmed into batteries and some pass-throughs. You choose how long to heat your atomizer with the manual button. You probably could modify your existing pass-through with a manual switch. I just converted a Puresmoker penstyle pass-through that went wonky this week into a manual. Much improved device, now.