When I clean my plugin with TES5Edit by filtering for cleaning, then running remove "Identical to Master" Records, it spits out this:

Upon further investigation I have discovered that those three cells are apparently empty. Not surprising as it's easy for the CK to create extras surrounding playable area in small worldspaces.

I suppose the CK creates a temp children group for all cells, empty or not, then TES5Edit removes the group if it's empty? Seems to be benign, at least. Any info from someone who can shed some light on this would still be appreciated, but I suppose I can just ignore this one. (or put something in those cells... or try to delete them entirely)

It's a holdover for an issue with Oblivion that would incorrectly process water in an empty worldspace cell. At least that's how I remember it. So the cleaning function was updated back then to deal with it.

So far as I've seen it's unnecessary for Skyrim but won't hurt anything if xEdit removes the data.

This happens to me too everytime I clean my Gray Cowl mod, in a tiny worldspace where I don't need terrain LOD. TES5Edit cleans my mod from my mod... From what I understand, TES5Edit removes empty groups made by CK.