Besides a rare defect in the brass of that case the most common reason for web thinning at the expansion web is excessive headspace. That excessive headspace can be caused by a chamber thats oversize or FL sizing the brass too far.
Set your FL so that it does not oversize the brass. So many think that they need to set the FL die to hit the shell holder. Don't do it that way. Set the die so that you can feel the case's shoulder just touch when closing the bolt.
Of course that round then may not fit another chamber of the same 'caliber'.
Make a feeler wire with a tiny 90 degree bent hook at its end. Reach into every case and feel for a insipiant head separation.
Set your FL so that it does not oversize the brass. So many think that they need to set the FL die to hit the shell holder. Don't do it that way. Set the die so that you can feel the case's shoulder just touch when closing the bolt.
Of course that round then may not fit another chamber of the same 'caliber'.
Make a feeler wire with a tiny 90 degree bent hook at its end. Reach into every case and feel for a insipiant head separation.
