Unable to log in in Tomcat 8.5.24 Manager even without user and password set

I work with an application which uses Apache Tomcat 8.5.24 in a Windows Server 2012 or superior as the foundation to run a webpage. I have already installed and successfully made the whole system work in accordance with the steps of an installation manual.

Lately I needed to install the system again in a client but, contrary to previous cases, I've simply being unable to access Tomcat's manager page ( with a browser.

I attempted many solutions found on the web on how to counter this issue, most of which involving changing the settings inside tomcat-users.xml, with no effect. I even came to the point of abandoning the idea of having a user and password set (the installation wizard says they are optional) and even so the pop-up requesting user and password keep showing and no manager is open. I did fresh reinstall even with a different installer (to check if it was corrupt), copied and pasted the tomcat-users.xml file from a different sucessfull installation, granted all possible permissions (the only real difference this time is that I'm installing remotely, but that shouldn't be a problem since the installation itself uses administrator rights) and the problem persists.

What other thigs could I try to solve this issue? Here are some links I consulted:

By the way, the Tomcat installation is unconnected to any NetBeans or similar software.