I had this same issue today while doing the Nazmir world quest ‘Burial Detail’. Fortunately I was able to dismount and engage in combat, but every time I would remount, I would experience the same issue as Uematsu.
Also, while taking the flight path from Forlorn Ruins to Zul’jan in Nazmir the flight mount did not appear and I was just floating through the air by myself on the flight path.