We have two Windows 10 machines, both running Scrivener. On mine I get a rectangle for a Shift-Enter. On the other, she gets a right turn arrow, for lack of a better description. What is wrong with mine, it should be the right arrow icon. I can put the images up to a URL and post them here if needed.
Are you using the same fonts on both computers? The square sounds sort of like when a character set doesn’t include something and just leaves a square/rectangle in its place. Could be that the “invisible” characters come from the font being used and not the default system font, or that you have different default system fonts.
I think you are correct, it is some sort of font issue. We’re both using a Georgia italic font and I looked at the systems fonts and they seem to be the same, but are clearly displaying differently.
I’ll keep plugging away at it. If I figure out why, I will post the result.