Sync error with tasks

[nomore66201]

[Server Information]
Ubuntu Server 16.04, Radicale 1.1.2 behind an NGINX proxy

After adding a Task on my PC with thunderbird (version 52.1.1), DAVDroid gives me the following error: debug.txt. Before that, DAVDroid was working fine, even if I modified (not created) a task with thunderbird. The task where originally created all on Android with OpenTasks.

If I remove from thunderbird the new task, the problem goes away, and I'm able again to synk with DAVDroid

[rfc2822]

Can you provide the contents of https://somewhere.com/asd/calendar.ics/20170406T064355Z-8d48d734dcfaf04.ics?