I am hosting several CalDAV calendars on my Synology NAS that I access with Lightning (and Android). This worked well until a few days ago, when the IP address of my NAS changed and required the reconfiguration of the CalDAV URLs.
Unfortunately, I do not get some of the calendars activated in Lightning on some some of my devices. The are greyed out and if I tick “Switch this Calendar on” it only takes one second and then it is gray again. The strange pattern is that not all my devices are affected by this, despite that I use exactly the same URL. And one of the Calendars is always “on” while the other two are only “on” on one Win7 laptop, while “off” on one Win10 laptop and a Win7 desktop. All my PCs should run the latest version of Thunderbird with integrated Lightning V.18.104.22.168. The NAS runs DSM 6.2.1-23824 Update 1. I do not have any issues with the Android device.
I would appreciate if there is any hint what I can do to get the calendars activated in Lightning.