Today I tried a little experiment. I changed the default printer to four different printers. The document displayed and printed identically. No change at all in line spacing.

This is a computer that I used when creating the manuscript over the period of a year starting in 2017 and then made multiple edits since that time. It is only now that the problem has occurred. I am the only user and I have made no changes to the machine.

Things I haven't mentioned: I am an electronics engineer so I do understand the hardware involved very well. Also, the laptop which displays and prints properly is having serious hardware issues. So, I may soon be left without a computer on which to edit my manuscript.

That means I am becoming a little desperate. If anyone has another idea I would greatly appreciate it. And, thank you again to those who have tried to help!