Unable to add single ASIN to a parent listing

For some reason a few of my variations of my Product X are listed as single items in the catalog. I was able to assign most of them to my original parent listing that should include all variations.

But still some of the single items that have been split off won’t become childs of the parent that I have.

Any ideas on how to approach that?

I have head of “locked down listings” when a product has too many revviewwz or other reasons for not merging with a parent, is that the issue?