I recently had oil tank filling issue with one I serviced for this problem, cleaned Revoir screen, replaced check valve, pressure tested good, tank filled very fast when completed. After two trips out, same problem, tank half full.
Tank had pressure but no flow. Restricted screen and filter, oil looked good. However, it was not good.
filter.jpg
This is a reusable filter for a common coffee maker that I used to check the oil. A gallon of new premium plus will flow thru this filter in less than one minute. The oil in his would completely stop flowing thru it with about one qt
He uses nothing but premium plus new gallon jugs, oil did not appear abnormal at all. The boat had set without use for 6 months in his garage. There was a thick film collected in the filter that was gelled. In the tank this oil looked ok
There you go: test the oil quality as well when you have this issue. easy quick test with a $10.00 filter
PS:
Just remembered when first came in with the oil fill problem, I noticed a powerhead gasket leak which I did replace.
Thinking maybe the reason being a lot water introduced thru the intake and some of it being passed thru the crankcase check valve into the oil tank. Maybe enough to cause the gelling but not enough to be noticeable as the oil appeared to be normal