Curses, I forgot that the forum title won’t display certain characters too… :-(
Bad IT day.

(It's funny -- I read this yesterday on my iPad and thought, "what's so special about those characters then?")

Your problem has been reported a couple of times in the Adobe InDesign forums (which, by the way, you'd better avoid for a while as they appear to have some serious server malfunction on this Friday the 13th). Extensive communication only led to the OPs switching off ligatures, because that seemed to be the root cause of the problem.
I am not convinced about that, though.

... I am using Universal Type Client to manage fonts ...

Step 1 is to switch this off and see if the problem persists. Possibly it will, possibly not. Read on for further clarification.

Step 2 is -- either with or without UTC -- to check in what folder these font files reside; you can use Find Font's "More Info" button for that. Is the location some place you could reasonably expect?

Step 3, finally, is to scan your entire hard disk for other versions of this same font. You cannot rely on the file name for this; InDesign reaches into the files and uses the actual Font Family Name and Full Name, no matter what the file is actually called.

My reasoning is that you might have several different versions of the same font set of Frutiger, but with slightly different features. InDesign cannot handle same name/different versions of fonts and is prone to nervous breakdowns if it encounters these, rather than just popping up an alert.

Ah -- you can use the information from Step 2 to make Step 3 a bit easier :D

Step 2 will tell you which file(s) InDesign is currently using. So reach into your computer and make these files not-available (move them somewhere else, delete them, I don't know).
If InDesign still displays your file as if nothing happened, you know for sure it found the very same font set somewhere else.

Repeat this until ID finally acknowledges it cannot find the font anymore, because possibly you have more than two versions of the font as well! Then choose any of the complete sets you have and install only that one.

Many thanks Theunis, I will have a chat with IT about your suggestions.