I’m sorry you’re having trouble here @Carol, I hope I can help out a bit. The first thing to note in that direction of things is that we’re quite limited by things specific to the .ics calendar file format, which is an important detail because, for example, one of the format’s limitations is that it does not allow for paragraph breaks.
The break between that paragraph above and this one, for example, can only be “represented” in an .ics file, not actually rendered as such, and so this leads to the “nn” in your event descriptions because “\n\n” is how you symbolize a paragraph break in .ics files. If you look at the output of your .ics file directly, you will see these characters in the event description as shown in this screenshot:

You can remove those characters if need be, for now. We are working on better handling of characters like these in future updates for the iCal importer.
This is important because things relating to the file format itself are at play with your other and main issue, the one where end dates are not being added to events; your .ics files seems to be labeling all day events with a Microsoft-specific parameter “X-MICROSOFT-CDO-ALLDAYEVENT:TRUE”. This isn’t an .ics standard, so our plugin likely doesn’t have support for this at this time.
To be clear, does your event that is not an all-day event import correctly?