Fira Code Symbols not working for `true` and `false`

I’m using Doom Emacs with Emacs 28.1 on Nixos unstable with the packages fira-code and fira-code-symbols installed. In init.el i have (ligatures +fira +extra).

The symbols work in all cases except for true and false where only an empty rectangle is shown.

System information

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Screenshot_20220706_142907 Screenshot_20220706_142926

I can confirm the same behaviour with Iosevka Nerd Font (also installed through nix)