According to the documention on Dialog behavior, when one player interacts with the Dialog all players should be able to see it too. This doesn’t work. I’ve set up a test place for this bug: Dialog bug - Roblox
Expected behavior
Dialog interactions should be globally visible.
Dialogs have always ran locally on the client, so they haven’t been able to see it since Filtering Enabled was forced on.
Either Roblox would have to rewrite the system or you would have to create your own dialog system.
Then why does it say that Dialogs are supposed to be replicated to all players in the documentation?
it doesnt say that though…
SinglePlayer is only one player can speak to the NPC, no one else can til the player is done talking (client-sided)
MultiPlayer is multiple people can speak to the NPC at the same time but its also client-sided.
Read what it says for SinglePlayer.
Just forwarded this to the team! Thanks for the report 
