https://youtu.be/t85vYqyqX5Q
After noticing for a few weeks now that I am being automatically dismounted in certain situations in Cyrodiil (Gray Host), I was able to pinpoint tonight that riding through "ground heals" such as Extended Ritual or Channeled Focus from a Templar cause a repeatable automatic dismount. I did not test other effects on other classes because, frankly, the queue in Cyrodiil is too high during the Midyear Mayhem event to be bothered with that at that this time. Hopefully, this will be enough to launch further investigation. Thanks for your time.