every few minutes I see weird lines across the screen, it's still playable but annoying

I don't know what's causing this, but if it helps it's on a multiplayer server. it uses spigot but we weren't using plugins on it until recently, just one to moniter diamond ores to stone mined ratio against xray texturepacks. the bug was happening already before that. when I move my mouse it usually dissapears and something simaler reapears soon