FWIW, This does appear to be a Mac bug with Font Import.
The fonts imported on Mac were also “messed up” when used on Windows.
A quick “Reimport” on a Windows machine and all was fine.
I’m having this problem on windows 10, version 4.17. My texture will be working fine but when I reimport it’ll randomly do this and I’ll have to delete it and set it up again from scratch.