What happens if an author acknowledges a potential anonymous referee in the paper?

As an editor in both computer science and biology, I would generally consider a person listed in the acknowledgements to be involved enough to have a conflict of interest, and therefore would not invite them to be a reviewer. This is a heuristic, not an absolute rule.

It is also worth noting that I usually solicit a review from precisely one of the recommended reviewers, since recommended reviewers are often "close" in the network of the authors, and I want to have more independent perspectives as well. It's still worth listing multiple recommended reviewers, since some may be unavailable, but it's not useful (for editors like me) to make a very extensive list.

Nothing would happen. In my area (math) it is quite possible that X will end up being the referee in spite of the fact that you mentioned them. Providing someone with insightful comments is not considered to be a connection strong enough to constitute a conflict of interest, so the editor would not normally have any reason for concern.

I should note that in math, authors submitting papers for publication are not typically asked to suggest names of potential referees, so perhaps that makes the answer less relevant for you.