Can I ask what software you ran into that issue with? Probably, it was a strict-monospace environment, like vim in a terminal. I have created code-specific fonts to deal with this issue:

there are fonts made specifically for code which have code ligatures & the simple l, f, 6, & 9 frozen in, if you like these features but don’t want to mess with OpenType features (or if your code editor doesn’t support that).

https://github.com/arrowtype/recursive/tree/main/fonts/rec_m....

The issue doesn’t occur in web browsers, as far as I know, as they support proportional type (include mostly-mono families with a few proportional glyphs).