The iCalendar is invalid:BEGIN:VCALENDAR VERSION:2.0 METHOD:PUBLISH PRODID:-//Dolibarr CDav//FR BEGIN:VTODO … PRIORITY:80 … END:VTODO END:VCALENDAR A calendar object on a CalDAV server must not have a METHOD property. (Doesn’t matter here) PRIORITY must be an integer between 0 and 9
Your iCalendar contains PRIORITY:80, which is not valid and cannot be synchronized. Please fix your iCalendars.
Does that help?