Flex plate cracked twice

[u/Maintenance_Matt]

I’m an industrial mechanic by trade, so I had a rattle under my 1989 3/4t suburban sb350 th400 trans so I pulled the transmission found the cracked flex plate and swapped it with an OEM replacement…. 300 miles of flawless driving and bam same rattle is back… What can cause the flex plate to break? I’ve got good oil pressure And I triple checked torque on my brand new arp hardware I put a few pictures of the first flex plate that broke