I'm definitely not alone to defend NNBSP in French. There are lot os sources, and your problem for having it invisible on your specific device does not cauyse any harm even to you.
Your display is not broken/unreadable even if your device uses ugly fonts with ugly/overlarge punctuations with extra padding (in fact it jsut happens that your font maps this NNBSP to zero-width, which is coherent with the design of its ugly punctuations)
Change your font preferences in your browser (instead of the legacy fonts), you'll see the difference if you want. But that's not needed at all for the UI that you'll want to make discrete and compact, to leave more space for the content. It would be a problem if you saw ugly boxes for unmapped glyphs, but your browser does not even do that!