I had a similar thing recently and it was because I wasn't running the washer that sits on the freehub body behind the cassette. Is there any play in your cassette at all? It is a 0.5mm washer that you need ... but not on all cassettes? I didn't need one on my shimano road cassette, moved to a shimano mtb cassette and needed a washer on that weirdly. Was tricky to find in the end. Presumably they come with the cassette when you buy new but I bought it off here so didn't I have one.
I need to have a proper inspect of everything and take it all apart but i'm 99% sure the washer is in place and no play in cassette. I'm going to go from 11-42 + hanger extender thingie down to just 11-36 and no extender - it'll be interesting to see if it magically sorts itself after that
I had a similar thing recently and it was because I wasn't running the washer that sits on the freehub body behind the cassette. Is there any play in your cassette at all? It is a 0.5mm washer that you need ... but not on all cassettes? I didn't need one on my shimano road cassette, moved to a shimano mtb cassette and needed a washer on that weirdly. Was tricky to find in the end. Presumably they come with the cassette when you buy new but I bought it off here so didn't I have one.