I switched my persona and the mount keyring did not follow. It also wouldn't let me claim a second of the same mount because it is already possessed.
When switching personas you need to zone to be able to see things like bank, keyrings, itemoverflow, etc. Try that and see if you can use it then. It worked fine in beta, I used the illusion, mount and teleport keyrings.
I zoned a few times before I tried to use the mount. Even switched back and forth. The second persona doesn't show the mount in the first persona keyring. I added another mount in the second keyring after trying to see if it'll fix.
