Motion and FCP do not handle font-related problems well – corrupted font duplicates, corrupted font cache and other similar issues cause these apps to display errors.

You can fix such problems using mInstaller: close Motion and FCP, open mInstaller and uninstall the product that you are working with. Next, go to mInstaller's Settings via the Cogwheel Menu, [Fix] the fonts, reboot your Mac, and install the previously removed product again.

Note: all fonts that mInstaller will try to repair are copied over to Mac⁩ > Library⁩ > ⁨Fonts (Removed)⁩ folder.