I notice two things:
https://sh3ll.cloud/c/ad/68.json shows there are 5 topics in this category.
But the category is named “ad” and I supposed it could be because these topics are advertisements removed by a browser ad-blocker.
On my default browser which uses an ad-blocker, I see no topics on your link, exactly like you.
Using Safari, which has no ad-blocker by default, I see the posts:
I’m not 100% sure this is the cause, but if it’s not, that should give enough clues to help pinpoint the exact cause 
edit: oh, I replied but apparently didn’t see the screenshot in lilly’s post 
edit again: that seems to be the issue:
My adblocker adds a display: none !important; on these elements:
I think many adblockers look for the “ad” word. Using a different name for your category may fix the issue.