Google Docs documents constantly update as you add or edit them. If you have a document open twice there’s also a visual indication of that (a marker).
I’ve just experienced a situation where neither occurred.
That is, I had the same document open in two different windows. When I became aware of that & went to close one I noticed that it had not updated with the latest text I’d typed in the other and that the marker that shows that the document was also open at another location wasn’t displayed.
I don’t know whether this is a GDocs issue (never happened before) or a BRAVE issue.
But I do know that if I report it to Google I’ll just be told that BRAVE isn’t a supported browser.