Font substitution issues

My hard disk crashed last week, got a new one all set up and working except:
I use three fonts in my writing, Garamond, Copperplate and a specialist symbol one. Everything is fine except in my new installation has substituted Helvetica for the specialist font. All three are installed and work correctly elsewhere. How do I substitute my specialist font for Helvetica.

I sync between Mac and iOS scrivener - the font is fine on my iPad, until I open it in the new installation on my mac then it becomes Helvetica.

This sounds a good deal like the issue described in this recent thread. In the end it turned out to likely be a bad user folder migration, but we don’t know for sure.