I'm having this same issue. Its not everytime I play but it happens at least once everyday. The lag is severe until it simply crashes my console. Also, i can't stand playing split screen with my kids because it lags very terrible. I hope this gets fixed because it's been a problem since the new update.
I hope you implement a different solution instead of killing off all immortal mobs. Maybe if they are name tagged, they wont despawn when the new update drops but they will be normal again.
I'm having this same issue. Its not everytime I play but it happens at least once everyday. The lag is severe until it simply crashes my console. Also, i can't stand playing split screen with my kids because it lags very terrible. I hope this gets fixed because it's been a problem since the new update.