Certain unicode fonts display improperly on MacOS

I haven't been able to reproduce this issue on my Mac, but my users have emailed me screenshots showing the bug. I'm using a QTextEdit in my program, and all the other font looks I've used look fine, but with only one particular font (Galatia SIL, a well respected Unicode font), only on certain Macs (just under half of my users, some users with the absolute latest version of MacOS have the issue, others don't), I see this issue when displaying Greek text. This is definitely another vote for moving to Harfbuzz on Mac, as I've had quite a few font/display issues on Mac with my heavily text centered app (at least 3-4 current bugs in Qt in how the Mac renders text that aren't in either the Windows or Linux versions). So after spending much of the day trying to reproduce this one, I can say I would beg/plead for Harfbuzz on Mac!