"Charlie" wrote in message
news
Could it be cutworms? When you find a cut off plant, start scratching
around in the soil, working out from the stem and see if you find one
of these little bastids...

I have never seen these, but I don't suppose that means they aren't there.
I am guessing it's earwigs, though--they are ALL OVER the place.

The collar should protect seedlings.

Welp, that's what I wanted to know! Thanks. Hopefully you are right.
--S.