Originally Posted by PTahCha

The ability to use GE lane and kiosk has nothing to do with KTN - that's related to PreCheck. After all, not all airlines participate in PreCheck and ability to store KTN in the PNR. However, for US-inbound flights, they are required to transmit the passenger manifest an hour prior to departure.

Your GE or Nexus profile is tied to your identifying document, which for most people would be your passport or PR card. Could it be that the GE membership has expired, or a new passport was issued, but the GE profile was not updated? That would cause a mismatch, and it has happened to me in the past. Once the new passport information is updated, then it was business as usual.