The LOTR-movies in the box set with the barcode 7333018017948 are all missing.
The reported barcode is correctly linked to the appropriate LOTR collection, and all films in the set have the correct IMDb links.
Is it possible that you added the box set as a single entry? If so, I recommend removing the box set from your personal database and adding it again using a barcode search. When prompted, select “Add Box as 3”, and the individual movies will be imported with the correct film information and IMDb links.
I hope this helps.
Hmmm… Perhaps there was some kind of error from when I changed the edition from single movies (Special Extended DVD Edition) to this 4K Box Set 
Because I never added this box as a new entry…
However, I just tried to link each movie to the default edition in Core and it worked. The IMDb-link is now present again 