This issue applied to GoDaddy and a move to Sitegrounds and I'm getting the same issue.
My primary domain sits in the root public_html folder. I have a htaccess file using admin tools there.
Setting up new domains they have a folder structure like this public_html/{sitename}/
My problem is whenever I setup a site the root htaccess file causes a 403 error on the new site.
Not a clue where to start