I had the same experience several times upgrading a B fare or W fare using miles and SWU.

When I apply for an upgrade and NC=0 I'm put on the wait list. When NC clears I'm not transfered to NC unless I call united. I have to use KVS tool to check the status on NC almost daily before my flight.

However when I apply for an upgrade and NC > 1 the upgrade clears immediatly.

Therefore the person who applies for the upgrade first is not the one that gets the seat.

NOTE: 4 hours before international flights all available seats on F and C becomes available as NF and NC. By this time the upgrade list is already under airport control, and they seems to follow the rules. First clearing by status than by order of upgrade applycation.