Arabic fonts not displaying properly (not a RTL issue)

Since updating to the latest version of Photoshop around half of my Arabic fonts no longer work, displaying only .notdef glyphs even when I can see the correct glyph in the glyphs panel and click on it. All of them had been working with no issues on the previous version I'd been using (CC 2018) but it seems possible that I had ensured that by messing with preferences in some way that I don't remember.