Whenever we play two player games (on the same console, same internet), the system lags. The lag happens when another players opens a chest, gets into their inventory,  or trades with a wandering trader or villager.

It also doesn't load for awhile when going through portals. It takes awhile to go and come back from the Nether. Sometimes while it's loading, we hear ourselves being attacked, losing health, and once loaded nothing is there attacking us.