It's been some time now, but some of the dialogs don't show up. I've seen that this doesn't happen in everygame and I'm wondering how developers are dealing with this.
Do you mean when an NPC has dialogue? Or when you press "/" it allows you to type?
If you mean NPC,
Right click on the NPC's head (explorer), and click insert>Dialog, and then right click on that, and insert>DialogChoice. Add as many DialogChoices and you want. I suggest having the "Properties" tab open, so you can modify the text.
If you meant the actual chat.
Go to the game's page, click the "Gear" icon, and then Configure, Permissions, and then chat type. Classic - On the left in the box Bubble - Over the player's head Both - Both, obviously.
Hope I helped.