I found an archived four month old thread on the matter at https://community.wanikani.com/t/Weird-radical-six-on-lvl-39/14928 and just wanted to see of some new light have been shed on this.
I just reached level 39 and one of the radicals is 六. This radical is not currently used for a single kanji on any of the 60 levels so I am quite intrigued as to what the purpose is. And why on level 39? The plot thickens…
For the lazy, the page for the radical looks like this (the “Marked Items” sections is a user script):
Not a big deal at all, just a peculiar conundrum.