I had the same issue, though I am running FM8 on Windows 10. Everything was fine up until the Creator Update that Windows installed in mid July, at which point the only text symbols I could see were the paragraph markers. No non breaking spaces, markers, soft returns etc.
Following the update I noticed that some fonts I had installed on my system were no longer available, meaning that FM was reporting missing fonts in documents. When I tried to reinstall these fonts, Windows said they were already installed, but I reinstalled them anyway and that solved the problem once I restarted FM.
I tried this same approach with the fm5font.ttf font located in the fminit folder, and once I had restarted my computer, everything was back to normal.
So, my solution was to reinstall fm5font.ttf, then restart the machine. Good luck.