In other applications, I've seen flexible tubing and hoses "delaminate" internally. Sometimes the bad section will appear normal on a low flow rate, like when you are using a garden hose to run water through a 1.5" flex hose, yet when you apply higher flow rates during suction, the bad section closes off most of the diameter of the hose.

Can you swap ends on your connections and check it that way? My guess is that it will act normal then. If it does, replace it.