Broken powerline rendering in Konsole 24.01.75?

As you can see, it renders correctly in Kitty and Wezterm (plus vscode, and Konsole 23.08). All fonts are set to (unpatched) JetBrains Mono 10pt. I also have some nerd fonts installed. So it seems Konsole somehow can’t fallback to nerd fonts while other terms can? How do I debug this kind of issues?