let me give you an idea how to check if ISP causing this.
When you guys make maintenance and the server on but no gamers online make a speedtest.net and 100 pig on internet providers ip, then make both again after 1 hour later with gamers, then 1 hour later again, do this till server have heavy traffic. this is the best tactic to check if the internet providers causing this. if you see a lot down and upload in last test, then come back here and post the result, i feel the download and upload in heavy traffic will be low.
1 Question, all server share 1 internet? or all sevver have diff? or like chronos and naia share and the 2 classic share, so there is 2 internet 1 for live and 1 for classic?