At the dawn of Commander time, it was a somewhat common issue. The bolts used there were originally 10mm, then upgraded to 12mm. The worst part is, of course, removing the broken bolts. If threadlocker was used, you may need to use heat to facilitate removal. I believe loosening and subsequent movement is what led to failure. Some replaced with higher grade bolts, but I think replacement with use of loctite (red) was the ultimate fix.