I don't know is my answer as I have never attempted chair rail. It looks like a lot of wood for the bit to cut. Did you take a couple or more passes to get the final profile? The 1st pic looks like a fairly clean cut. Pic #2 and #3 show the wood being ripped out more than being clean cut. My 1st guess is if you didn't take a couple of passes the bit dulled. Guess 2 is cutting against the grain.
I am interested in the correct answer myself.
I am interested in the correct answer myself.