The server sends an invalid event:
Caused by: net.fortuna.ical4j.data.ParserException: Error at line 11:Invalid UTC offset [-500] - must be of the form: (+/-)HHMM[SS]
I suggest to download the “remote resource” with the browser (same credentials as for CalDAV) and then have a look at the event, especially in line 11. Then you can fix the event or just delete it and enter it again. You will also find the origin/creating program of the event.