Underscore does not display in Courier for Zoom above 116% (FrameMaker 10)

I have a new Lenovo T460  laptop with Windows 10.

I normally write with zoom at 140%.

Now statements in Courier font within InformalExample and Example elements do not display unless I reduce the Zoom to below 117.

They disappear as soon as I increase the zoom to anything above 116.

The underscore displays under all zoom settings in OTHER elements that do not use the Courier font.

When typed in a Courier font, the underscore is present but does not display when the Zoom is > 116%.

Also, the underscores no longer display in the content that existed in documents created on my old laptop.

The underscores do not behave thus when Zoom is modified  in Word or Excel.