those characters probably relate to carriage return &line feed characters.
It does not happen on the test site http://test.icalevents.com/event/event-with-new-lines-etc/ or on my local host.
Sometimes these things are due to another plugin filtering the page and/or post content. Try disabling other plugins till problem disappears. That will tell you which plugin it is.
If you are referring to the ics output, then note that 'folding' the lines is required by the ics rfc 5545 specification.
Content lines are delimited by a line break,
which is a CRLF sequence (CR character followed by LF character).
Lines of text SHOULD NOT be longer than 75 octets, excluding the line
break. Long content lines SHOULD be split into a multiple line
representations using a line "folding" technique. That is, a long
line can be split between any two characters by inserting a CRLF
immediately followed by a single linear white-space character (i.e.,
SPACE or HTAB).