Are you wearing super-stiff shoes? I had a set of carbon Shimanos that were super-stiff, and I had toe numbness all the time. When they wore out, though, I replaced them with some Sidi Genius 5 Pros, with a carbon composite sole instead of a carbon weave. No issues since - apparently the little bit of flex was just what I needed! It's not enough to be at all noticeable, let alone cause meaningful power loss, but it sure is comfy.