Link to Core

I have some movies that are in Core but when I follow the Help I get the following screen:

There is no Link to Core button, only Update from Core. This screen also appears when I have added movies manually. There is no option to Link to Core, nor any option to link to a different bar code. Am I doing something wrong, or is this a bug?

That looks like the action bar when you select movies.
The “Link Movie” or “Unlink Movie” is only available per 1 single movie. And only above the details page.

Want to link/unlink 1 movie?
If you wish to link/unlink one single movie, use the 3 dotted button above the details page. (the black bar). That has a link (or unlink) button.

Want to link all unlinked movies?
use Link Movies from the main menu top left under “import/export”

Excellent. Thanks.