Check that your derailleur is low enough that there's daylight - 1-2 links of chain free between the upper pulley and sprocket. Often a misadjusted B screw will have the pulley touching the cassette through the chain, causing the RD to get kicked back because of interaction between the two.

Also double check for any stiff links, by backpedaling slowly while pushing the lower pulley forward to slacken the lower loop.

Lastly, it could be a cassette spacing, RD trim issue. Sometimes the spacing isn't dead on, and with the jockey wheel so close there's no room for the chain to flex enough, and it'll ride up on the edges of the teeth. This is most common on new cassettes, as later the chain rounds off the tops of the teeth making engagement smoother.