Does the new user "userB" belong to the same set of groups as the old user "userA"?
More details here: https://serverfault.com/questions/947301/nginx-displaying-failed-13-permission-denied-when-trying-to-access-new-site
Basically:
- Check user permissions on the public directory -> You said userA and userB both have access.
- Check that the new userB belongs to a group with
rxaccess to the public directory for the website.