I found this problem when I typed < ’ > in a text box.
It displays like the following image.
From my own experience, it seems like I’m typing a symbol that can not be matched from the font library.
I’m using the Mac’s U.S. keyboard, the font is Helvetica, and my system language is English. (I tried so many different fonts, and it happened to most of them.)
Please let me know if you have any idea of why it happens and how can I fix it.