A long shot :
Is the Windows 10 display scale setting set to 100% ?
Since Windows 8 introduced this setting years ago, there were several display issues reported with FileMaker Pro when the setting is not at the original size.
Not a long shot at all!
Problem solved by setting the display to 100%.
to whom it may concern:
this behavior is known for a couple of other rendering issues and also prior to FMP 14 and prior to Windows 10!