However, when you first load into the battle on a refresh of the page, you'll get correct data. Once you attack though, the overlay will show the wrong mons until a reload, but then repeat the above.
It turns out UBlock on Chrome can prevent the extension from working in some cases as it seems to block something. May be a good idea to have a troubleshooting section that adblockers like Ublock some functionality.
https://i.imgur.com/OsaAAhK.png
However, when you first load into the battle on a refresh of the page, you'll get correct data. Once you attack though, the overlay will show the wrong mons until a reload, but then repeat the above.