We have also seen this issue with being logged in to the gateway.
We use docker for development, so when I want to compare two gateway settings, I had them both open. But every time I logged in to one, the other was logged out.
These gateways were completely isolated, but shared the same ip address. So it’s not related to the gateway, but to how the browser and the session cookies interact. A cookie works per ip address, and is shared over all ports of that ip address.
Our solution was to use private mode (since that stops sharing the cookies over multiple tabs). Or in Firefox you also have the feature “Multi account containers”, which will limit the cookies to a certain number of tabs.