If the solar nebula theory is the correct explanation of how the solar system formed, then what is the likely cause of two planets being highly tilted or rotating “backwards,” and one planet not revolving in the same plane as the rest by more than 10 degrees?

I don't think everything was as neat and orderly as we imagine it to have been when all the loose material began to coalesce. There could have been outside forces still at work affecting the formation of the present solar system.
If the solar nebula theory is the correct explanation of how the solar system formed, then what is the likely cause of two planets being highly tilted or rotating “backwards,” and one planet not revolving in the same plane as the rest by more than 10 degrees?

Because God wanted it to :)

If the solar nebula theory is the correct explanation of how the solar system formed, then what is the likely cause of two planets being highly tilted or rotating “backwards,” and one planet not revolving in the same plane as the rest by more than 10 degrees?

One explanation is that during their formation Venus and Uranus were struck by large planetoids causing Uranus to be tilted and Venus to have its rotation retrograded.

The only object classified as a "planet" with an extreme elliptical non-plane orbit is Pluto. That's one reason why it's suspected of being a Kuiper belt object. That's the same area surrounding our solar system from which comets are thought to originate. Such objects are pulled or jostled into extreme solar elliptical orbits via coliisons among themselves or or close encounters with a hypothetical passing star.

Actually, the majority of extrasolar planets discovered have extreme elliptical orbits. So perhaps ours is a very rare exception.


BTW

I agree with the opinion that all this happens because God wills it to be so.