exactly, the real question is what the elves are doing while they’re unseen.
I can answer the what, that parts easy!
The real question is WHY they keep stealing my underwear and left-foot socks?
We should've asked Terence McKenna...
It could be a subspecies of the "machine elves"...
Making toys, caring for reindeer, sleight maintenance, ...
And spook work for His Jolliness' Secret Service, to keep their Naughty and Nice databases current.
They keep the universe running.