Confluence calendar subscribe link is empty

I have found today that when I want to subscribe to a team calendar, the "subscribe link" is empty. (It is on a cloud instance).

Moreover my already subscribed calendar in thunderbird are now disabled (the link I used to use seems invalid now (error 400 when i try it with chrome).

I have tried creating some new calendar, resetting the link, or adding restriction but no effect.
Is it a temporary error on Atlassian server or is there something todo?