Is the actual url being shown? Or are you changing it to hide your domain?
I tested both the fqdn as well as the local ip address https://pass.domain.com/auth/login and https://10.0.0.21/auth/login
They both return the same results. That’s when i knew something is not running as it should be. For example: passbolt can be installed and tied to a domain name, the server should still be able to access the passbolt server directly using the local IP assigned to it.
I will be going to site in the next 30 Minutes as i need to physically be there for this one, Will update you on the configuration files on how I have setup passbolt. When i get there 
Thank You
JamesBond