Since this has been posted almost a year now, I was wondering on the status at Instructure. I have recently been contacted by more faculty with this exact issue. Their feedback looks great when they view it, but when students go to Grades and view Comments, it is one big block of text with no formatting. One instructor even tried to use a list for the students but it came out looking like a long sentence with a bunch of hyphens on the student end.
Currently I recommend using more than one comment in lieu of paragraphs, but that does not help a list much. Usually we are all using Chromium browsers on Windows or MAC computers. Some students are using various mobile devices as well.