So the problem (for me) stems from the upgrade of Nerd Fonts from 2.2.2 to 3.x, there were some breaking changes in the codepoints for some icons due to clashing with non-english languages. You can see the tracking issue here.
I verified this by quickly downgrading nerdfonts to 22-11’s stable release, which fixed my broken glyphs/icons immediately.
To use 3.x versions, I fixed all the illegal codepoints in my own code using nerdfix. You can interactively scan and replace illegal codepoints in-place with