Update: I looked at the LH support app this morning and saw that wait times were down. Gave them a call and actually got someone in less than 10min. The rep validated that everything looks good on their end and all segments are confirmed, but still mentioned that the ticket needs to be reissued by UA.

Gave UA a call and walked through the situation. The agent contacted the ticketing desk and after a while got a concrete answer back: UA cannot reissue the ticket until 24 hours before the flight. Once the window opens, I need to give them a call and have it reissued. Otherwise, everything looks good. Upgrade will not be cancelled and I should be good to go.

TomMM I'm not sure why this option was available either... to be fair, I haven't booked anything on LH in a while, but if everything clears properly, I effectively saved $800 on an upgrade by doing it directly through LH.