If you refresh the page, the old page should be destroyed before it can get the session close notification;
but if you open a new page on a different browser, the previous page is supposed to receive an invocation in onServerError, notifying error code 35.
It is strange that you didn't see anything.

We have to trace what happens.
Please reproduce the case on a dedicated Server instance, by opening only the two involved pages on two different browsers.
To keep the logs short, you should also prevent the pages from performing subscriptions, which are not relevant in this case.
As a first step, show us the Server log, taken after setting LightstreamerLogger.push at DEBUG level.