I have set up my game to register the player using device ID on initial login. I have also provided a method of registering to Playfab account. Upon doing so, the device ID will be linked to the playfab account.
The issue I see here is that any currency that the player may own while they are on the device ID account will not be carried over to the registered playfab account when linked.
Im using Unreal Engine 4 just for reference.