Before reboot

After reboot

I don't use multi-screen. It's a plain old Dell xps-15. It worked before the last insiders (slow ring) update (though it's called something else now?) and I don't recall having made any changes or added anything.

As I said, I don't reboot that often, so not a biggie :)

Couldn't see anything in the post that you referred to that could make a difference

Okay, I use a vertical bar on the right and it's a black theme, sorry, but hopefully you can see the bar width:

Before reboot

After reboot

Did you need the entire height? No worries I can do that if you need it.