I am not sure if you can call this a bug. My definition would be that x11 handles such things different than Wayland.
To help you and without telling you “use Wayland instead”, I would like to know what keeps you using x11?
Have you tried to put the left screen (in settings) on the same height as the big one?
This could be the reason not seeing the top bar.
And you have to switch the option on to see the top bar on both screens. I guess you made that?
When you have dual screen, you mostly have the option to choose on which screen do you want the Top Bar alias menu Bar.
Som DE’s give you the option to switch it on on both screens.
p.s.
It looks like you are still using x11? Or do you have Wayland in Budgie too?