Sooooo... Clearly NH has some room for improvement if any pax finds their process to be non-intuitive. But, speaking as a very frequent Asia traveler, this whole post strikes me more as an "I'm not used to this" sort of thing, moreso than any actual problem with NH. There's a few gems in here that would have made OP's experience better.
a) Being able to check-in more than 2-3 hours in advance is not common at many Asian airports. Most have an "Early check-in" area or desk where, with certain restrictions, you can check in prior to the desks opening. In some (like SIN & BKK), that area is a designated office in the back of the check-in gallery. In HKG, you can use the in-city Airport Express desks to check-in as much as 24-hours prior to your flight (and drop bags!!) But otherwise yes, ANA clearly publishes that their desks at HKIA open 2:30 prior to the flight.
b) UA's app _always_ prohibits seat changes on the reservation inside of 24h. Doesn't matter if it's Int'l or Domestic, once you're T-24, you have to use the Check-in / already-checked-in app and website features to make any changes. Itinerary view won't do anything. And since your initiating flight was operated by a partner, yes, you have to check in with that partner, not UA.
c) The ANA official lounge in HKG is the United Club. Can't hardly blame NH (or UA) for bathroom problems or bad mobile signal in the SQ lounge... but even if you choose to, the reality is that Gate 24 is literally about 50 yards further from the UA club as from the NH club! Remember that gates on that central pier jump from 36 to 60, at the "Y". So it's not like you actually would have had to walk past ~30-some gates to get there...
d) As another poster mentioned, UA does NOT always park at a gate. I've had to bus to a hard-stand for UA before, but also as noted, they prioritize long-haul over short-haul. I don't think I've ever had a UA TPAC flight depart from a hard-stand, but when they were operating SGN / SIN, absolutely! TYO is short-haul, so it's not unheard of. Consider yourself lucky that most of *A never uses the 500 gates!!
Then you have a bus AND a gate wait!
Can't speak to problems with NH OLCI... the few times I've used it, I've never had an issue. But from just zipping through the rarely-crowded ANA priority desks ~90-120 minutes prior to departure, I've never had reason to poke at it too hard!!
Sorry you had a bad experience OP, but you sort of made some weird decisions there. Virtually all of them could have been avoided with some prior experience in HK/Asia.
