Mine always tend to root a wee bit, once the goodness goes from the grass (autumn time) but not usually their entire field
I'm wondering if, now the boar has arrived they'll have something to keep them occupied
It might have been boredom ?
A neighbour ringed his Kunekunes after they started rooting (each to their own, but mine aren't ringed) It was small rings along the upper edge of the snout. They didn't stop them rooting, it actually made quite a mess of their snouts and I'm sure at least one got ripped out leaving a bit of hanging skin.
Do you have an area of hard standing you can move them to for a while ? I'd also try putting some hay or hayledge in for them too - see if it distracts them
HTH
Karen