Distance to problem?

Hmmm… to many broken variable references ( this method only sends the actual level BP, not all the associated widgets etc ).

Can you make a small project with it in and give me a link?

To make the project, just

  1. Make a new empty first person project
  2. Migrate your level ( map ) to that project ( right-click on your level file and choose migrate )
  3. Zip that project up ( File → Package project → zip up project )

It should only be a few hundred MB.