Yes, please contact the WiFi providers. I also recommend to use HTTPS URLs which can’t be intercepted by WiFi hotspots (you will get a cert error).
Once every few weeks my calendars from icsdroid disappear and I have to add the URL to the app again. I’ve missed a substansial amount of reminders because of that.
Had never happend to me, and without any further hints I can’t say anything about that. Maybe a 3rd-party app which is messing around with calendars?
I use DAVDroid and OpenTasks on the same device
I can comfirm that my calendar also disappears in the app.
I also use DAVdroid + OpenTasks + ICSdroid on a Oneplus3 with LineageOS 14.1.
I have the same problem. Also have DAVdroid + OpenTasks installed with LineageOS.
Is there any way to do a backup of the calendar settings? I tried using Titanium Backup, but was not able to restore the settings after all calenders disappeared.