Can't get Di2 rear derailleur any where near position

Recently had a chain jam whilst riding and now while fitting new chain di2 adjustment won't get anywhere near to position. The H adjustment is maybe 3 sprockte inwards from the smallest sporcoket and the L screw is at atleast 1 sprocket inward of the biggest cog. My initial reaction is this is a bent hanger but feels strange that the limit screws won't get near to either the biggest or smallest sprocket! Any ideas?!
Inside the mech is a sort of knurled collet that positions the mech. If you yank the mech it can move the collet round snd from then on you mech will always be put of position to where it thinks it is.