EDIT: posted at the same time strobro posted his response.
Call Richard and he'll weld it up for you.
It happened to my M11/22 ejector plate twice. In my case, I believe that it was due to the plate not being perfectly snug (front to back) in the upper (which was my doing). When it was firing, the plate was moving back and forth a little and putting stress at odd points. Once I got rid of the play, it has run like a top showing no indication of stress. It also now runs any ammo I can feed it; before, it would only run RGB.
Or have strobro weld it, he'll do a good job

Richard said I could weld mine myself, but to be aware that alignment is critical. I chose to have him do it since I don't have the best welding skillz.