Calendar with Thunderbird/52.7.0 Lightning/5.4.7 observations

First I attempted to configure Lightning by pointing to a top level 
calendar URL, iOS is able to autoconfigure all but Lightning fails.
Then I configured Lightning by copying long Calendar URL from calendar page.

Connections seems fine but
1. Lightning is unable to view current events, list is empty.
2. Lightning can create new events just fine - they appear in Web UI and 
iOS clients.
3. Lightning can't see Tasks, apparently I need to create another 
calendar and use a URL from Tasks page - will try it later, seems odd.

Unrelated to Lightning only I see in /var/log/httpd/error_log for all 
CalDAV clients.
... [core:notice] [pid 514] AH00052: child pid PID exit signal 
Segmentation fault (11)

I wonder if anyone is using Lightning with kolab and how to find out the 
segfaulting process.

--
Regards,
Josh.