Our chosen monospace font unfortunately has a big functional problem; it has ligatures enabled by default. That means it fails to uphold the principle of all characters having the same width, as sometimes characters will get merged.
The issue has been discussed several times upstream, but without a released fix:
Fortunately, there is a workaround for CSS at least, in that we can disable ligatures using:
> font-variant-ligatures: none;
This needs to be done wherever we use Space Mono.
✅ Font ligatures are disabled for instances of Space Mono in tlwebadm and tlwebaccess
Confirmed for all instances of Space Mono in both web services.
✅ Font ligature behavior is retained for fonts other than Space Mono, in tlwebadm and tlwebaccess
The other two fonts, Mulish and Poppins, don't seem to exhibit any font ligatures.
I agree with the conclusions in comment 2.