More often than not a reservation that is out of sync was when someone would hold space for an upgrade but be required to surrender a paper certificate at check in. The un-synced PNR would thus inhibit checkin and require the agent to do an add/collect.

Further expanding on the add/collect a fare difference or a modification that changes a segment, class of service, or moving to OA, the reservation is then out of sync from the original ticketed reservation and thus need to be re-synced to be put in the ticketing queue. In your case the upgraded class on LH PNR needs to match your UA PNR and vice versa.

The steps to resync are simple....that is unless you have someone that doesn't know SHARES.