That looks like neopreme hose, if so check for a flapper inside the hose, sometimes the fittings will dig out a piece of the inside of the hose so it acts like a flapper valve blocking the inside of the line. Remove the hose so you can see inside the fittings with a strong, bright light and see if you can see one, also try taking a real thin ice pick or thin knitting needles to push inside the fitting and slide it into the hose on all four sides to see if the needle or probe pushes the flapper out
I'm facing a intermittent fuel leak in my system now, I'm thinking it is the nepreme bypass hose from the pump to the tank leaking after it runs a while and gets some warm fuel ran thru it. I hope to find it tomorrow, I'm going to put it on four jackstands and run it for 5 or 6 minutes to see if it will start leaking again