Reopening of an existing chat after a page refresh or navigating through it is based on cookie LaRunningChat.
When you load a page where there is a chat button integrated and during this loading, the chat finds cookie LaRunningChat with valid data, it attempts to load the existing chat and connect to it. It works like this both when refreshing the page or navigating through it.
If the cookie is for any reason erased or empty, the existing chat won't reopen.