I've been told it is possible to downgrade but that I should have really good backups. That is good advice as something always seems to go wrong when I start big tasks without the proper protection in place.
I updated the ticket regarding the calendar issue for those that are interested in what we've learned.
https://portal.smartertools.com/community/a87715/calendar-problems-after-upgrade-to-version-14_5_5871.aspx#94447
For some reason I couldn't get the link function in the post editor to work...