Are you sure you have a gap between the casing and the frame? There should be a little gap otherwise you are bending the casing and possible causing the crank to bind
The only place it contacts the frame is at the bottom bracket shell which is standard for installation. Since the motor casing is actually independent of the spindle I don’t know how one can affect the other. Mystery!!
I did my first install of a BBS02 over 12,000 miles ago, and have removed, serviced and reinstalled countless times since then. It’s not installed incorrectly.