So when I shift from the middle sprocket to the smaller on the front, the chain will sometimes get caught inbetween the two sprockets. It helps if I shift it fast (grip shift), but it still does it sometimes. I haven't noticed a difference when clean or dirty either.
I think it may be the front derailleur, but I really don't know.
It's an xt crank and front derailluer with a sram 9.0 shifter. Not sure what kind of chain.