So unfortunately the move to https effectively got rid of all of the Facebook comments as well as Social Media share metrics. I say effectively because even though they don't appear anymore, they still exist. This previously also effected any entry, photo, or video who had their name changed.
I want to recommend again that the field be changed to a static one so that each page that gets renamed doesn't hide all of the comments again. Seeing as how https://knowyourmeme.com/meme/[id] redirects to the current page name, we could use that as the standard for entries, photos, and videos and see if comments disappear. I'm pretty sure comments are tied to each profile and so unless the profile is deleted, the comment will stay regardless of the url.
Another page also recommends adding:
<meta property="og:url" content="http://example.com/post-url" />
to the head so that you can preserve share metrics, but if we use "https://knowyourmeme.com/meme/[id]" then we could possibly preserve future metrics to negate these name changes destroying further metrics.