1) I was running the sewers with a friend when they died after someone joined. They ended up booting them, saying them joining had caused them to lag, and therefore die. I can't be certain if they stopped moving because I myself had just joined and was still enroute.

2) Same friend, different game. They were lagging really bad in Hideout and asked everyone to turn off push notifications. I automatically say no when asked to enable every time so i know i didnt have it enabled. A little bit later, still lagging, this friend boots a player and states that after booting them their lag decreased significantly so it was that player.

Now, I know these all happened to someone else and this is outside knowledge, but here's 3:

I was leveling at CtK when another player joined. I literally froze. My ping started skyrocketing so I exited the game and rejoined. While completing the run I had numerous pauses due to ping lag, even with a green dot. In all my previous runs there was no lag.

So, can other players cause you to lag and if so what are the main causes and how can you avoid/identify it?