Can’t Join PS4 Worlds On An IOS Device

When I play on my friends world who hosts the world on a PS4 sometimes I can leave the game and then when I try to join back the world will not appear. When they try inviting me when this happens I don’t get an invite. Even sometimes when they leave the world when I’m in it I can’t join back. Basically i leave the world and I can’t join back because the world doesn’t appear. This has been happening for about 2 months now.