I had that happen to me on my MTB after swapping out the BB for a sealed unit and having to modify (shim) the front DR to reach the outer ring. It came loose just enough to move (pivot) and throw off the alignment with the chain. After having the chain jam in the rear, I looked it over and sure enough the FDR was guiding the chain at an off angle to the rear cassette and binding the chain back there. I realigned the FDR and all is good with the world again. If I hadn't recently shimmed out the FDR for the reach, I never would have suspected it. Just another thought. Good luck,