I seem to recall in the past when checking in via the United, it would check you in for all the legs - including any partner flights. When I went to Zurich in December, my 3rd flight was on Swiss Air and the app would not check me in for that flight. Also, I could not check in on the Swiss Air web site. Eventually, a nice lady at the Polaris Lounge at IAD was able to do something and get me a boarding pass.

I have a trip coming up this week - TPA-IAH-NRT-HKG where the NRT to HKG leg is on ANA. The ticket was booked on United, and I can see the full Reservation on My Trips on UA.com, and the ANA seats I selected on ANA.com are showing up correctly on UA.com.

Will the UA App check me in and give me a Boarding Pass for the NRT to HKG leg?