The standard Bafang crank arms are not substantial.
After about 275 miles, I have noticed the cranks "distort" a bit under higher torque pedaling. The left crank has become loose twice and re-tighten. It may have been do to my often used technique of mounting the bike with foot on pedal while pushing off.
I purchased the Lekkie Buzz Cranks 170mm that are more substantial and also solve the "Q factor" issue.
When they arrive, I will do a review.