I would love to see a screenshot
Thank you for your post.
I am unable to replicate the issue using FileMaker Pro 14.0.2 under Windows 10. I also tried formatting the field as Checkbox and all characters are displayed.
Is Settings -> System -> Display set for 100%? If not, set it for 100% and see if the issue still exists.
A screenshot might help here. I'm curious as to whether the letters are getting cut off on the right or on the left. I have seen letters get cut off on the left, particularly when the "classic" theme was used. Try adjusting the left/right "padding" in Inspector to see if that helps.