#2 Aug 26, 2018 15:20
'Uncategorized' is the category b2evo creates by default if you don't create any categories explicitly.
The main category will always also be an extra category.
If you deselected "uncategorized" (main & uncheck "extra" checkbox), then your post in no longer in the uncategorized category.
Nothing is baked into the slugs, unless it is in a web-cache that hasn't refreshed yet.
Please posts screenshots of your issues. "I get a message about cross posting" is not precise enough. Do you have multiple collections set up?