The filter bypass valve can certainly open in cold start-ups. Jim Allen (member here) did some real world testing on his vehicle with pressure gauges mounted. All filters need a bypass valve, either built into the filter, or built into the engine ... otherwise the filter could become damaged if the delta-p becomes too high.Bypass pressure is simply Delta pressure. So what’s going out can’t be different than coming in. If so then it can’t surpass the bypass other wise it opens.
People claim that at start up the bypass opens. I’d like to see these claims as many manufacturers don’t even have a bypass. My Hyundai Elantra. While my Subaru does.