Hey there! I just got rid of that problem. Here’s what I did:
Go to template-tags.php in the Editor.
Go to line 232 (or just search the page for “vantage_get_archive_title()” and it gets you to the right line).
It should say “$title = sprintf( __( ‘Category Archive: %s’, ‘vantage’ ), ‘<span>’ . single_cat_title( ”, false ) .”
Take out the part that says “Category Archive:” but nothing else.
Your problem should be fixed then! Before you change anything, it’s helpful to copy and paste the original into a Word document or txt file and tuck it somewhere in case you ever have to go back to the original.