I see that too. File an official report via Special:Contact.
Looks like that page was deleted. I don't get the error, so it was probably a transient backend caching problem.
They deleted the page just now, but the same problem appears on many pages in the wiki.
I would assume you had some bad experience with Fandom staff in the past? Yet, they do help most of the time, and having wikis working properly is absolutely their commercial interest. Also, it's unlikely that anyone else would be able to help.
Okay, I see it now on the Emma Swan page... I did some experimenting and it looks like the problem is that UCP can't handle the infobox...
This is almost certainly a UCP migration bug. I'll bet if you remove the infobox the page might be okay (although that's not what you want).
The issue is that some pages won't even let you edit them. Instead of getting the error message on the page like in the image, you just get a browser error message. But yeah, this is definitely something only staff can fix.