Context: Friend had been playing a bit, I started and went into the tutorial. During the tutorial, he joined. We were using Discord for voice.

Steps
1. Friend who joined game marked two enemies
2. Immediately dropped from about 28-30 fps to 1 for a time
3. Frame rate stayed below 10 until unmarking
4. Stick frames every time sync shot status changes, such as marking another enemy, aiming at marked enemy, etc.


Notes:
Often did not occur for just 1 marked enemy by friend
Steady state even with marked enemies frame rate returned to normal
Only when aiming, changing marks, etc did sticky frames occur

nvidia 1080gtx, default video settings.