Hi!
Thank you, I can access the editor now, however it did not allow me to make changes.
Fortunately I don’t need it anymore, as I spotted the issue by accident, when I check the Snippets you had active. There was this snippet: https://i.imgur.com/V6VnlxV.png
Since WooCommerce 3.0 the product visibility was moved from custom fields to taxonomies, and that snippet no longer works properly. I have simply deactivated it, and excluded the hidden products taxonomy as described in the updated knowledge base.
Now it should be working all right.