Short story: it's not Linux, it's Rogean's networking cleverness/fuckery (which term you use depends on whether you're having issues with it or not ATM
[You must be logged in to view images. Log in or Register.] ... but unfortunately, because of insane ex-players that attack the P99 servers, no matter what you call it, it's necessary).
There is an open source app, P99 Middleman D, which used to fix this ... but for me (also on Linux, Linux Mint specifically) it stopped working like a year ago.
The solution I found was to get a VPN. It costs $5 a month, will (almost certainly) fix this issue, and it will let you download bit torrents without your ISP sending you nasty letters.
But, if you're on a limited budget, or philosophically opposed to a VPN ... well first get a VPN anyway, at least on a free trial, just to confirm that it fixes things. But then once it does and you've confirmed the networking stuff is the problem, you can start going through the laundry list of settings on your router that could be to blame.
There's other threads for that laundry list in the technical chat. Good luck!