Number400, I just checked my double chain set bikes and both FDs, RX100 and 600, have a purpose made bend near the tail of the FD's cage to move it inward. The Sora may just gradually bend the whole cage, but it would be best to compare with a known good Sora double FD.

Depending on how close the chain set is to the seat tube, chainstay length and other possible factors the off set from the larger chain ring to the smallest cassette cog can be enough to derail the chain. I'd first suspect a laterally stiff chain or the chain is not flexible laterally at some point along it's run. Shimano chains assembled with their special pins can be very stiff at the joined links.

Brad