Actually, it means "waitlist KLearing." It comes between PA/PB and HK. As a gate agent, my ticketing skills are pretty dormant, but I'm pretty sure there's nothing for you to do. Either the computer just takes some time to switch your status, or some res agent takes care of things.

I'm 100% sure of the meaning of KL, and that you'll get your upgrade, but I'm only about 10% how this KL creature works.

...a UA GA