This system has been used for years to anchor heavy equipment to FLOORS where there is relatively little tensile load on the joint and where you are assured that the epoxy is well contained while it sets up.
This would probably be the worst application for this type of a fastener in that a full bond could not be assured particularly given the field installation methods.
I cannot say what the design specification was in this application, but I would not feel comfortable with less than a 5X margin of safety (but then my supervisors have always deemed me to be conservative). Should one of them fail, the adjacent fasteners must take up the load. But given your description of the panel, it is more likely that several of the fasteners failed simultaneously over a period of time. I.e., a poorly designed application for a marginally installed product.
From what I heard, the workers faild to clean out the holes after they were drilled, so the epoxy bonded to the dust.