I've been using the Lightning extension for last 5 years. After upgrading to Thunderbird 38 (current version is 38.2.0), I have to manually enable my network calendars from the Properties box every time I open Thunderbird.

Is there a solution to this problem? A workaround that I found that sometimes works is switching to the Offline mode and the reverting to the Online mode. This way, the calendars are enabled when I open Tbird, but for couple of hours only.