Access Denied or not have sufficient privileges to access its data

I use a viewer's account and try enter a new site, the account does not have permissions of the site.

When I try enter the site, Appian alerting me to display  "403 Access Denied You don't have permission to view this page.",

sometimes, an error is popped "An Error Has Occurred The Site xxx does not exit, has been deleted, or you do not have sufficient privileges to access its data."

if I use designer's account, All are ok.

I expect to display only one case - “403 Access Denied You don't have permission to view this page.”