Foreman doesn't (and can't) autoload exported blueprints.
Since Factorio 0.15 i also disabled exporting as a string, since i think the new vanilla format should be used.
Foreman used to export to /script-ouput/blueprintstring/username. So searching your PC for script-output should show you where it is (depends on your operating system, on Linux it's in ~/.factorio for me, don't know about Windows/MacOS)
