CORS errors when editing a block in dev mode

I have started building my first ACF blocks so naturally I want to test a lot in the block editor while I develop.
I can log in to the localhost:3000wp/wp-login and both the core blocks and 'normal ACF fields seem to work fine so far.
However when I try to edit an ACF block (created with ACF-Composer) I get CORS errors.
Requests to are blocked

What could be the cause of this?