HL means waitlisted. In the old days, partners would put an award flight on waitlist pending some review/confirmation. I seem to recall many (like 20+) years ago this happening when I tried to use AA miles on a partner. I was told to call back in 24 hours as the agent felt comfortable it would be confirmed by then. Now-a-days most award programs do not allow waitlisting (though some do for their own operated flights).