I experienced this "phenomenon" during the recent KODH and after some googling, learned that there is a proper term for it - "Chain Suck". This is when the chain clings onto the chain ring and gets lifted up a full circle, jamming the drive train. Usual suspects are wore chain and worn chain rings. On close observation at home, my chain looks fine and all 3 chain rings up front look fine too. Then I read this write up which I think could be my case. Chain suck can occur to perfectly working chains and chain rings. Chain suck usually occur in front, when shifting from the middle chain ring to the granny chain ring, during hard forceful pedal stroke up steep slopes. The forceful stroke can bent the chain sideways and diagonally downwards to the granny chain ring if shifting is done at that time causing the chain links to cling tightly onto the middle chain ring and jamming up the drivetrain. As the jamming occurs forcefully during pedal up steep slopes, damage may occur to chain, chain ring, front and rear de. The solution is to avoid shifting in front from middle chain ring to the granny chain ring during forceful stroke. Maybe there are already better parts out there that can deal with chain suck...