Help! No monsters are spawning if I have 3 players in world.

I have a 3 player vanilla survival realm and everything has been working fine for 100-200 hours of gameplay until this past weekend. We noticed that monsters suddenly weren’t spawning when all three players are in the game. If one player leaves, monsters immediately begin spawning. It doesn’t matter which player leaves the game.

Things I’ve tried:

• Set game to peaceful for some time (force all hostile mobs to despawn) then back to normal difficulty.
• Player 1 was playing on PC and tried switching to Xbox X.
• Player 3 has a child account: age was set to 21+.
• Tried eliminating many non-hostile mobs in case we were near the limit.
• Tried downloading the game to my Xbox and hosting locally. Still no mobs even though Realms wasn’t involved.

We are playing Bedrock edition 1.20.51. This is my son’s first time playing survival and he is super invested in our world. We are all frustrated that one person has to log out for the others to fight monsters. Please help!