Problems with outbound traffic - socket failures.

An OVH Windows 2025 bare-metal-server, and are having no end of trouble with FTP to another site.   

Fetch HTTP - no problem;
Files via FTP - no problem ... but the original connection fails 1 in every 6-7 connects.

RDP (remote desktop) is now not working either.

OVH are not answering tickets, can't get hold of anybody.

Testing so far suggests it is something to do with the OVH network blocking/dropping packets.

Anybody got any insights/clues/how to diagnose?

Can post powershell test scripts, and results.

Any help appreciated!