Players teleporting and yellow square icon in Breakthrough mode

I have an RX 5700 XT, Ryzen 7 2700X, and 32 GB of RAM. I play on high settings — for example, in Rush or Deathmatch everything runs smoothly.
But in Breakthrough, it’s almost impossible to play.

I keep getting a yellow square in the top-left corner, and sometimes a circle with an arrow.
Also, both friendly and enemy players keep teleporting around the map, moving very abruptly.

Can anyone help me figure out what’s causing this issue? Thanks!