Cannot display iCal calendars anymore

How to reproduce:
try to display a calendar as explained in the documentation here
https://extensions.xwiki.org/xwiki/bin/view/Extension/FullCalendar%20Application#HPrivatecalendar28Since2.129

expected result:

• the events are displayed on the calendar

actual result:

• the events are not displayed on the calendar .

Note: not event an XHR request is made to actually fetch the events.