Puzzling fresh water pump issue

[LouSlugger]

Last summer we towed our rig to Michigan with empty fresh water tank and filled it at local gas station (with RV dump station/water) there, then on to nearby state park (with no water supply). Once at campsite, no water would come out of faucets or elsewhere, even though pump was running. Checked for blockage in filter and did everything else I could think of to identify problem but no luck. After returning home, local servicer "repaired" problem, telling me there was a crimp in a line. Didn't make sense to me but system was working again. Fast forward to this month. Before towing to campsite in Tennessee, put about 30 gallons of fresh water in and confirmed all OK. Get to Tennessee, top off fresh water tank during one night stay at KOA, then on to campsite (no water supply). Guess what? Same thing as last year: pump working but no water out of faucet. Completely drained tank before return trip home. Scheduled mobile service to come to my house to diagnose. Partially filled tank ahead of time so tech could do his thing, and...started working again. So it appears that something happens when I top off the tank that prevents the system from working properly. Does this make sense, and has anyone else had similar experience? Thanks.