Stash completly reset after trading

If you did not use the "Migrate All" option, then any items in your stash would still be in the SSF league where they were left.

If you'd like to migrate these as well, you'd want to use the "Migrate All" option, or alternately you may be able to use the manual league migration button found at the bottom of the character select screen (it's the button with ">>" on it).