Hi Adam. It looks like your client can’t access the fonts database on your Mac. Can you determine what happened when the client stopped working correctly? Did you update NoMachine, upgrade the OS, installed some 3rd party apps that could affect Mac standard behaviors?
You could check if the font chooser lets you select anything. Click the Settings button under NoMachine logo, select the second icon in the left column (Player), and the second icon in the right column (Appearance). Once there, click the first button you see on the right column and try to select a different font, or let me know if the chooser is empty as well.