Maintenance for the week of January 12:
• [IN PROGRESS] ESO Store and Account System for maintenance – January 14, 9:00AM ET (14:00 UTC) - 12:00PM ET (17:00 UTC)
Was just about to report the same. Picked it up today and in both the store animation and after purchasing it, there's a delay of 1-2 seconds when both the mount and character disappear immediately after summoning.