I came across this oddity today where I was going to print a report someone sent me and the data didn't appear to expand all the way to the right. My printout was looking like the below screenshot with a huge right margin space!
After fiddling around for what seemed like forever in the Print Settings, I discovered that the Print Titles section was causing the issue.
After deleting the Columns to Repeat at Left range, my print margins appear to return to normal.
I have no idea why this occurs but hopefully, this post prevents you from continuing to pull out your hair with this weird margin issue.