Ubisoft's stance on this is - it's all on YOUR end, not theirs.
DO NOT expect this to be resolved. They have your money, your enjoyment means NOTHING to them now.
You can jump through their hoops, networking, firewalls, resets, reinstalls, MTU adjustments, etc etc etc... but at the end of the day, even after it's been working fine for years, the only response you'll get is "Talk to your ISP."
Again, they have your money, you have their paper weight.