When I checked the email in Outlook, I got a tiny info message saying "Extra line breaks in this message were removed" and the option to restore them. Gmail gave no such indication (that I found) but I must assume it removed them as well.
Interestingly enough I had line breaks elsewhere in the body that worked as expected, only the ones in the loop were deemed "extra".
I have modified my code to build the email body using html.
IsBodyHtml = true
If anyone knows of a way to prevent this, or what causes certain line breaks to be removed, please let me know.
Update:
Once I knew what I was looking for, I found this post which helps to explain things and gives some alternate solutions. I did not try any of them, as I think using html is the better solution in my case.