511 of 512 waypoints
Latest waypoint added to the game was in Lion’s Arch, by the portal that was added to lead to Durmand Priory/Lornar Pass.
Before that was a new waypoint added to Lornar Pass for the Marionette LS.
If it’s neither of those, you could mouse over every map and see if any of them show 98-99% completion instead of 100. I know there’s one such off the beaten path wp in Harathi, with no areas of interest nearby, but it does count for Harathi completion so if you got that 100%, the wp should be unlocked.
Have you gone to all WvW maps? They count too for map completion.
checked there, thanks for the tip. found one I missed completely in black citadel