The shaft is subjected to combined bending and fluctuating torsional load.
I don't believe the stress concentration factors for a grooved shaft that you cited apply. In those cases the inside radius of the groove is 1/2 the groove width.
In the case of the snap ring groove in question the...
Power transmission shafting on conveying equipment that was purchased from a sub-contractor is failing at a snap ring
groove. The snap ring grooves are used to position a drive
sprocket on the shaft.
I need to check our sub's shaft design but can't find a
source for snap ring groove stress...