Welcome to the forums @Palerite!
I have not encountered this myself, so I'm not totally sure right off what could be causing it. It is strange that in the editor it looks fine, but some letters in game are closer (especially noticeable with C, M, and T).
Maybe try changing the font size just a little bit to see if that fixes it? Like if it's size is 42
, maybe setting it to 41
would work?