Chamfer sometimes has issues when the edges aren't smooth/tangent. which is the case here. you can see from the zebra analysis that the slots are crossing over face edges that aren't tangent to each other. You can also tell because the entire loop of edges isn't selected with one click, even though "tangent chain" is selected in the dialog box.
extrude 14 created one of the problematic faces because, outside of the body there isn't normal to the extruded face. As a bit of a cheat, I was able to delete that face, just to see if I could get the chamfer to work. I would suggest going back and fixing it properly with the sketches though.
I also used the pattern command to do the slots and chamfers, which I think is generally a better approach than using sketches, but that's up to you.
