Well OVH is crappy for customer support so I will probably never get any answer regarding the outage.
Or they will just plain lie about it.
If you want to know more:
1) The dashboard for monitoring the server said it as online the whole time.
2) When I tried to create a support ticket it did not work until after 1h into the outtage
3) They did not answer the support ticket (still open)
4) The weathermap of their datacenter never showed anything (all green, no servers down anywhere) for the whole duration of the outtage
5) I know for a fact (From their incidents page) that almost 250 servers were down for almost 7h for the most unlucky ones. But in the incident those servers were in another room of the datacenter (not where my server is). Still the weathermap was green for the whole duration of the incident...
6) I tried a cold reboot thinking it was my server alone having a problem. Twice the automatic answer was that the server was not pinging after reboot (OVH monitoring page still saying everything was OK) and that a tecnician will have a look (never had).
So their monitoring sucks, the weathermap is a lie and the support team never answers (or not correctly).
It was actually my offsite (not at OVH) monitoring that alerted me the server was down.
They are just awful... But cheap and with a good network.