Second embedded web browser session won't open

We have a specific RDM setup where the RDM gateway server is acting as a Zero Trust server, meaning users have to go through the gateway server to access applications such as Splunk. This is enforced by firewall.
I'm able to open a first browser tab in RDM fine. It doesn't matter which server I choose. However, if I open a second browser session, regardless of browser and regardless of the server chosen, I get a blank screen for that second tab. If I close the first browser session and attempt the session I previously chose for the second session, it opens just fine. I don't see this issue when opening multiple SSH windows, and I am also able to open other applications that are allowed access without going through the RDM gateway. If I disable the firewall rules to allow user access to Splunk without going through the RDM gateway, for example, I can open up multiple windows just fine. This issue started just recently without upgrading version or any other changes that I'm aware of.