This would be a rough issue if you’re park hopping. You could exit Disney with an existing reservation for DCA and then not be able to re-enter
Disneyland because it’s unavailable. If you didn’t check ahead of time you could exit BOTH parks and be screwed stuck in the middle waiting for reservations to become available again.
I think if you scan in once you should be able to jump back and forth all day and maybe only be considered “gone” (and thus needing a new reservation) if you’ve been out of both parks for like 2+ hours.