Maintenance for the week of March 16:
• [IN PROGRESS] ESO Store and Account System for maintenance – March 18, 6:00AM EDT (10:00 UTC) - 4:00PM EDT (20:00 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.