Are you talking about the list in the left rail of the Lead Database screen?
I have not had to log out of Markeo completely, but I have had to leave the Lead Database, let that left rail populate with other data, then come back before the list would appear.
Typically I'd import while in "Lead Database" then switch to "Marketing Activities", then back to "Lead Database". Sometimes I can switch to"My Marketo" and the newly created Import List is the top item.