Originally Posted by
ExplorerWannabe
The issue appeared to stem from the communication between airlines so if OP wants to fly on LH, I'd book with LH rather than UA. I don't think the reservation on LH would have been lost if I'd booked through LH -- and conversely (and sort of to your second point), UA does a better job IMO of recovering when an error has been made so if the roles had been reversed, I think UA would have been more helpful and successful in fixing it before my day of departure.
The problem appears to be related to the upgrade and ticket reissue which, yes, can definitely get messed up when two airlines are involved unfortunately.
I have flown many all-LH metal itineraries booked through United (where I was not using upgrades) and everything has gone 100% smoothly.