[Mashiro]

Yes, that was the conclusion from the topics. What else would one be able to conclude when a) the provider says everything is working as it should and b) you perform tests inside the VPS, open ports, check everything and all comes back good?

Sounds like a issue "higher up" above the provider at upstream level which is OVH. Neither side is going to do something though as a) the provider says everything is working correct and b) OVH will not do anything unless you upgrade to their game DDoS protection.

That's actually the thing. Normal OVH DDoS protection is not suitable for filtering game server traffic and might therefore even block it. So you can test all you want inside your VPS... it's of no use when it is getting blocked at upstream.