I've just checked https://www.wikidata.org/wiki/Q98668689 and I don't see the External Properties section. Neither logged in, nor logged out. So it looks like this was added by a gadget/user script. That means the gadget/user script doesn't add the right classes.
Can you tell which gadget/user script adds this section?

I think it's a user script. This looks like the one in https://www.wikidata.org/w/index.php?title=User:PKM/common.js:

importScript('User:Magnus Manske/ext-props.js');

It is indeed that script by @Magnus.
It looks bad too using Legacy Vector, so Magnus has to check/fix this. Isn't related to the new Vector skin that is being developed.
@PKM it is best to leave a note on Magnus' talkpage as well.

Note left on Magnus's talk page, thanks for checking.

It’s caused by aa45edd2f29b81b059d6856e945011cccbd81545. The user script should use <div class='portal vector-menu-portal' instead of <div class='portal'.