Originally Posted by stevel610

Wondering if the metal you are showing is the dropout or a steel protective piece like shown here. Your picture looks to be missing the rivets which might indicate a missing piece. Torquing the aluminum directly could stress in unusual ways.

Originally Posted by Broctoon

They’re not rivets, but tiny screws. The outer doubler plate has threaded holes, and the inner one is dimpled for countersunk screws, with 2.5 mm hex (Allen) heads.

I hope these were in place for the OP. If not, and he rode without them, I think we know why cracks appeared.