What's wrong with tables in VisualEditor? I'm trying to add a table to my page but the table comes out all wonky after I save changes. Most annoyingly, one of the columns becomes an enlarged caption, a few of the cells gets shifted all over, and I have entire sections of rows just missing or scrunched up into another row. The hell?
The issue is the "+" some of your cell contents have. For some reason, VisualEditor is not wrapping all of them in nowiki tags. You can either do that yourself or add a space in front of them so that they don't get misinterpreted as caption content.
To summarize, the UCP is a new version of the current platform, MediaWiki. However, there are so many differences between the new and current versions that the new one is essentially a different platform when it comes to the user experience. Starting this past Wednesday, all new wikis are created using the UCP. As more features become available to UCP wikis, pre-existing wikis will be migrated from the current platform to UCP. In the end, all wikis will be using the UCP.