When we turn on the LAN game and someone joins us, the monsters suddenly disappear. When the same person comes out, the monsters appear again

Sounds like MC-137795.

Maybe because that person who is joining is on peaceful difficulty?

Will it be fixed that the player will be able to travel separately and the monsters will appear?

It also affects randomTickSpeed. The best thing to do is to vote on MC-137795.

this command does not change anything