The issue was imported raw materials and manufacture items were side by side so you could not separate imports from manufactured when putting supply lines in.
So by moving the two apart this fixed the issue.
Now you can import raw materials on one line and manufacture them. Then supply them from your manufactured line
It makes sense for it to be in it’s own topic for now, I suppose. Although with the new rules to select to use only local products, it’s kind of obsolete.