As an update to my previous post, the problem still persists under Linux (Fedora 23)
using Thunderbird 38.6.0 (with Lightning 4.0.6) with several ical and CalDav calendars
(to three different caldav servers).
I disabled the ThunderBirthDay Addon, because it was almost unusable with it enabled.
It works fine for several hours, but I have to restart it once a day to be usable
(and responsive) again.
As an update to my previous post, the problem still persists under Linux (Fedora 23)
using Thunderbird 38.6.0 (with Lightning 4.0.6) with several ical and CalDav calendars
(to three different caldav servers).
I disabled the ThunderBirthDay Addon, because it was almost unusable with it enabled.
It works fine for several hours, but I have to restart it once a day to be usable
(and responsive) again.