Any idea what causes this?

Mine sheared off yesterday. New rifle (a build not factory). About 200 rounds through it.

I ordered a lost parts kit from Bushmaster that has 2 retaining pins and 2 retaining pin screws plus the take down pin and spring that the back plate keeps in place. Brownells had individual parts available also. Colt and DPMS.

Any idea what causes this? I have an H buffer in carbine stock. Cycled reliably up to now. Pin moved up and down normally to install/remove the buffer and buffer spring prior to breaking off.

Probably just a random occurance but thought I'd ask.

Thanks!