It does look from the picture as though the cage spring isn’t doing what it should be. But then, the whole mech looks a little odd. I was going to say that you could bring it over one evening and I’d take a look, but you would drive right past Steels to get to me. Anyway, the offer’s there.
I’ll be going up to Thrunton on Thursday morning for some riding and trail maintenance. I could meet you over there if you like? I’m fairly confident that I could give an accurate diagnosis if I had the bike in front of me; although I can’t guarantee being able to fix it in a car park with just my multitool!