Where you're running two Players on the same PC, you need to create a different Display Settings Profile in the CMS for one of the two Players, that gives a different local webserver port.
You do that under Display Settings in the CMS. Once you've created the profile, assign it from the Displays page by editing the display and setting the different profile.
If you're using Docker, then XMR will be running on port 9505. You need to enter the XMR address in the CMS settings page (XMR public address) as for example,
If you're not going to use XMR, then you don't need the port open, and you should clear that field in the CMS settings so that the Players don't try to connect.