This may sound strange, but can you try visiting the site with the graph on it in a Private window? I have a feeling there’s some background shenanigans with Brave’s protections happening.
Not super convenient but at least its on the board with high priority. You’ll likely see this fixed in an update in the near future.
I’d suggest using Private Windows for this task for now or, you can download the Beta or Developer builds of Brave and see if the issue presents the same way.