I’ve had about 10 of these occur since I downloaded today’s update. Twice it occurred taking the flight path from Boralus Harbor to Mechagon, both of which resulted in me being dismounted. Luckily I landed in water both times, so didn’t die.
The other times were after clicking portals to go somewhere: Boralus to Silithis, Dalaran to rogue class hall, Dalaran to Argus. In those cases, I just don’t go anywhere, keep clicking and eventually the port is successful.
Edit: after getting the bug again using an Argus transporter, I exited the client, which I hadn’t done since before the patch. Restarted and used the Argus transporter several times and then used the portal back to Dalaran and no issues. Fingers crossed that it was the client.