SSF -> trade migration in end game means no atlas

When I migrated my character from SSF to trade league, I couldn't access the atlas anymore. The character had already completed the campaign, so there was no way to reobtain it. I tried beating the Act 6 final boss again, to no avail.

I ended up migrating everything, which did work. But now my SSF progress is totally wiped and that's a bit of a shame.