
When checking the encoding of the exported .ics files I noticed it was set to UTF-8 with BOM. I removed the BOM from the ics files via SSH on linux (sed -i '1 s/^\xef\xbb\xbf//' *.ics), making it simply UTF-8, and ics files were now valid again.
I knew something was wrong when after the latest vueminder update I could no longer import ics files to google calendar, or other calendars that read ics files. Removing the BOM from the encoding solved the issue.
I tried to submit this as a bug report via the software but it merely opens a blank chrome window when clicked. I figured posting it here was the next best step, especially if it helps others who are experiencing the same issue.