It just cleared itself
My '99 had the same thing happen twice -- once about 4 years ago and again about 2 years ago. The left front wheel has always been the last one to display. The two times it failed to display a valid reading, it displayed XXX and then the check tire monitor system message.
When I got where I was headed, I parked and shut off the engine. When I started up, the sensors all displayed accurate numbers and the error message was gone.
I think this error condition and a few others that have displayed potential problems but then vanished are attributable to the old computer catch-all line used when the technicians don't have any idea of what a problem really is: "Static electricity"... or something as transient as that.
I hope it's that way for your tire monitor system too.