Just a data point on a complicated itinerary, but the logic is working as expected:
MNL-GUM-(Hopper)-HNL-LAX-SFO with a overnight in HNL that doesn't connect to the next flight out; on a bulk ticket
UA wants an RPU for each MNL-GUM // HNL-LAX-SFO since the overnight in HNL isn't on the immediate flight out in the morning.
GUM-HNL isn't eligible, as expected, on the hopper, with an agent doing the upgrade manually.