Broken rocker arms two weekends in a row

How about a close up pic of the break.

My recollection is the SB rockers are quite thin adjacent to where the bodies are counterbored for the bearings.

My thoughts are, either the rockers are reaching the end of their fatigue life……..or the springs are going away and as a result, the Valvetrain isn’t as happy as it could be/once was.
If the springs are total “overkill”, then the service life of the rockers will be shorter.