Could be the grass, the move, or they may need worming again, or fluking.
If you can get a sample of the green poo and take it to your vets, they'll do a worm egg count and tell you what needs doing in that respect. Mine do it within a couple of hours usually, depends how busy they are.
My dad's just switched to Ryelands and the first ones he bought lived here for a month while he sorted out at his place - they are very cute and friendly