Not sure what the issue is, my zsh has no issue with my powerline font. Also made sure to test this outside of tmux as sometimes it can affect things. I just get questions marks where I expect any sort of symbol from powerline.
To make it usable I have to do this for now.
config set modules.commandbox-bullet-train.unicode=false
Also testing this over iTerm2 on macOS with this font "DejaVu Sans Mono for Powerline Book". Not sure what else I can try, and like I said zsh or oh-my-zsh rather pulls in the font just fine.