I'm using Equinox theme, but I don't think it's a gtk theme issue (before the new scrollbars, it was fine), it looks like the LibreOffice sets the height of this area according to the horizontal scrollbar. But I haven't check, how it looks like with Ambiance/Radiance, I'll do that, when I get to my desktop PC. You're not experiencing it with Ambiance theme?
I'm using Equinox theme, but I don't think it's a gtk theme issue (before the new scrollbars, it was fine), it looks like the LibreOffice sets the height of this area according to the horizontal scrollbar. But I haven't check, how it looks like with Ambiance/Radiance, I'll do that, when I get to my desktop PC. You're not experiencing it with Ambiance theme?