I still have the issue, and now it's permanent.
By the way, I just found a way to overpass it, by using a VPN software. It changes the routing path and do not go through this laggy IP address anymore and I get back my normal ping.
Just tried with a random VPN software, which is free for 5 days, and see the results:
Now I'll try to find a good VPN service, maybe NordVPN? Will see.
Hope it helps other frenchies around