Lag/stutters performance issues

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So I’ve been having these lag stutter issues when I’m in multiplayer. I’ll clearly have the upper hand and opponents shields lowered, just for them to turn around and presumably one shot me… Why is this happening? Some games are worse than others, but this is majority of my play. I’ve been playing halo since CE, I’m not too bad at this and will call my own faults mine. Anyone else getting this?