DIAGNOSIS The wing nuts are not properly engaged with the locking system. The cause is incorrect installation order of the components on the filter stem.
FIX Correct assembly order, from the filter stem up, is: Step 1: Filter element. Step 2: Rubber washer. Step 3: Upper chamber hole. Step 4: Plastic washer. Step 5: Wing nut. Tighten the wing nut firmly by hand until the rubber washer compresses and seals. The upper chamber should be pinched securely between the rubber washer below and the plastic washer above.
IF THAT DIDN'T WORK Check that the plastic washer is present. If missing, the metal wing nut will cut into the rubber washer and not hold tension.
HEADS UP Do not use tools to overtighten the wing nuts. Hand-tight is sufficient. Overtightening can crack the chamber or strip the plastic threads on the filter stem.