fi is basically phi, which is a single greek letter so I don't see any problems.

"Mac" sounds a lot like "Mike", so you must be right.

Also happens on Android (mobile device)

That's pretty funny; it seems you've run into problems with ligatures (fi is often rendered as a combined image, called a ligature). https://gankra.github.io/blah/text-hates-you/#style-can-change-mid-ligature is an interesting writeup about it.

I guess one of your five demands to Mike has been accepted!

You're an inch closer to headquarters than others :D