When I ran my 6-3 thru the LB I got couple spots like this it like a dent it does not go thru the outer gray covering it just like it got pressed to hard in the fitting
340.24
Bending Radius. Bends in Type UF cable shall be so made that the cable is not damaged. The radius of the curve of the inner edge of any bend shall not be less than five times the diameter of the cable.
Does the LB provide for this?
It may be a better solution to use a junction box.