From your description, it sounds like the text is unconcealed when your cursor enters the line. The recommended option to avoid this is:
This will keep characters concealed until you actually want to operate on the hidden characters in visual or insert mode. You can read more with
Since you linked to them, I'll explain what those PRs actually fixed. (I'm their author)
Before it was fixed, Vim would conceal characters, but line lengths weren't updated and mouse clicks acted as if characters were still visible. It made tag navigation in help docs almost impossible to use with a mouse, which I felt would make it difficult for new users to actually learn Vim. Outside of the help docs, the problem got worse when Unicode characters were involved, especially double width characters.
For example, if you used a mouse to click on the first
Y in your example (column 3 from your perspective), the cursor would actually jump to column 9. This is because that
Y is actually on column 9. From your perspective, the cursor will appear to be on the second
So, those PRs address an issue you would have in Vim if you enabled
concealcursor normal mode.