Lag issues with some friends (not everybody).

About 4 months ago me and some friends starts to have lag issue between us (before that time we played normally without lag or anything), but suddenly the problem appears, from nowhere, nobody changes his internet conection or company. At first we thought that could be a problem with ports, firewall or some addon, but no, we did everything even unsuscribe every addon and reinstall the game. Please help, we cannot play.

P.S: I forgot to mention that it’s a p2p server and some of my friends have normal ping (about 30 - 50 ms), but others don’t (over 300 ms) and we live in the same city.

I’m so sorry for my bad english. Thanks for everything