@geo_c :-
The clones can be quite fussy in some respects, though once you have them set correctly, they'll run solidly for ever.
This sounds like a hardware acceleration issue to me. Every Chromium-based browser I've ever run, has two settings that need investigating. In Brave's case, hit the hamburger menu button top right->Settings->Additional settings->System. You'll see a pair of options:-
The first one, you should always, always un-check it. Due to the tab_sandbox model the Chromium 'clones' use, the browser can be closed, yet an individual tabbed process may have been spawned in the background by something else during your browsing session.....and it'll carry on silently running in the background, gobbling-up resources. Unchecking this prevents that from happening.
The second one is more trial & error, really. On the old Compaq rig, with integrated GPU and only 3 GB of 'shared' RAM, I found everything ran smoother - for me - if this was unchecked. On the new HP rig, with all that RAM, dedicated GPU with its own RAM, and just generally much newer with a lot more resources & capabilities, I now leave this in the default, checked position.
Right from day one, the clones have always made use of a 'default', raster graphics process by which they render & draw the screen. In recent years, the Chromium Project have done an awful lot of work on how the browser uses available GPU processes, and how it optimizes itself IF these extra abilities are available. Consequently, if you have a dedicated GPU it's best to use them; if not, and you have limited resources, it's best to disable hardware acceleration.
Maybe that'll help.....maybe not. Let us know what happens, please!
Mike. 
