Followup note: When I tested this on a different computer, the Visual Editor worked correctly the first time I tried it. But after clearing the browser cache, all of the above problems appeared.

It had been a week or two since I used that computer on World Anvil, so this suggests that a recent change to the Visual Editor caused these problems.

Typo correction: In the Steps To Reproduce, where it says "something" in quotes, it should have an at-sign before the word. The at-sign got deleted by the editor.

Here are some screenshots showing the differences in the Visual Editor between old and new edit modes. (I had to switch to the Euclid editor to embed them here!)

at-mention, the way it's supposed to work:

at-mention in Old Version Edit - no popup appears:

slash-command popup, the way it's supposed to work:

slash-command popup in Old Version Edit - commands like Image are missing:

Popup for selected text in the new UI, with the Create Link button highlighted:

Popup for selected text in Old Version Edit, showing where the Create Link button used to be:

i did some testing and it looks like the entity blocks fully work.
there should be however an ability to hyperlink from the formatting toolbar when something is selected and the mention search is an issue

I am still seeing all the same problems as before.

I did see the /-command menu working correctly for a minute, but then I cleared my browser cache and now it's missing a bunch of commands, as shown in my screenshot above. It seems pretty consistent that clearing the browser cache messes up Old Version Edit.

Yeah, because you are clearing local-storage too and we read data from that, quick logout and login should fix that - as per the @ menu, there's something unusual there

Unfortunately, logout - login doesn't fix anything - commands like /image are still not available in Old Version Edit, or in this bug comment box.

I also tried logout - close browser - open browser - login but that didn't help either.

I don't know why it started working for a minute on my laptop yesterday. If I figure out what I did I'll report back.

There was more work to do, make sure to retest it now :)

This bug was fixed for a while, but sometime in the last couple of weeks the Visual Editor in Old Version Edit has stopped working again - same symptoms as described above.

It looks like this bug has been fixed again, it's been working properly for a few days now.

Thank you for your attention to this.