Bug Reports should be posted in the Report an Issue section of this forum.
I do not currently use Macs but what you report suggests that a Font substitution has taken place. A suitcase may have been removed or some other issue with that font suitcase has occurred such as a duplicate or damaged suitcase.
…or maybe the users are copying the text from another application with a different font and pasting it into the FileMaker field(s).
Thanks all. Your answers help me determined that the issue was that my Suitcase Font Application is acting funny. It has desactivated all my fonts for some reason.
Thanks again for all your quick replies.