On the road bike , Ultegra Di2 10 speed groupset .

when on the big ring , and 1 from the top at the back , the chain suddenly drops onto the small ring and at the same time pulls the front mech bracket out of the frame , rivets just pulls out !
Replaced the rivets twice and it happened again this morning .

what could be causing it ?
chain is not catching .

Bent tooth on ring
Bent chain link

thanks , found dodgy link in the chain but i had to open it earlier to get front mech out so not sure when it happened .