From my Windows 10 laptop I often connect multiple monitors. When I use Brave on external monitor Brave does not seem to forget the external monitor after disconnecting it. When I am on my laptop only, with nothing connected, Brave opens but not seen on my screen. The pinned icon shows it is open but not on my only screen. The only way to view it is by clicking ALT-SHIFT-M, then my arrow keys to move it to my only screen. Even after re-booting the laptop Brave still cannot forget the external monitor setting. I do not see other browsers behaving this way with my system, so believe its only related to the Brave browser as the cause.
This issue is fixed and should be available in the next couple of releases. You can track the issue here