I’ve been struggling with font crashes for a few years as well, I think there are a few other threads about it like: Occasional glyph crash and Typeface::createSystemTypefaceFor Leaks on Mac
The issue I see is that glyphs start randomly disappearing / getting scrambled and then shortly after the program crashes. Only caused by using memory font on macOS.
I’ve spent a decent amount of time looking into it, never been able to find the cause.