We had the same problem on our Half-Life server and we were able to fix the network connection issues and server lag by using this settings. Just add them to your server.cfg and restart your server: //network
sv_minrate "0" // Min rate for players.
sv_maxrate "100000" // Max rate for players.
sv_minupdaterate "4"
sv_maxupdaterate "100"
sv_mincmdrate 4
sv_maxcmdrate 100
sv_unlag "0" // Enable lag compensation
sys_ticrate "600"