Multiplayer Map Icons and Weapons not appearing in world

Platform: PC/Steam
Issue: Players joining host (clients) may not see icons for locations on the map, and may not see weapons or other placed objects such as scopes in the world.

Cause: This happens when the person who joins a multiplayer game (the client) first loads in to a map (either on their own computer or a map from a different host) where locations have been explored and items have been picked up. This then causes the host world to not allow weapons and other placed objects that have already been picked up and map locations that have been unlocked to appear for the client character that has joined the host map, even if the host and the client characters have not been to these locations or encountered these items on the host map before with their current characters. This does not affect the host, who sees icons and weapons and items placed in the world as normal.

Resolution: Have the client exit the host map, then use the same character to start a new map. Then, they can exit the new map and rejoin the host map, and all map icons will be unlock-able and weapons and items in the host map will be loot-able by the client.