DLC purchased on Legacy PS4 Edition prior to the release of PS4 Bedrock are successfully transferred from Legacy PS4 Edition to PS4 Bedrock. However, after signing into an Xbox Live account on PS4 Bedrock, owned DLC and marketplace content are not transferred to the Live account. Previously purchased marketplace content on the Live account are not available on the PS4 Bedrock and previously purchased DLC content (from Legacy PS4 edition) are exclusively available on PS4 Bedrock (when they should be available on all platforms associated with the Live account).
 

A screenshot from PS4 Bedrock with a Live account signed in. Halloween Mash-up purchase transferred from Legacy PS4 Edition to PS4 Bedrock successfully.
 

A screenshot from Windows 10 Edition signed into the same Live account as the PS4 Bedrock screenshot above. Halloween Mash-up purchase failed to transfer to Windows 10 Edition from PS4 Bedrock.
 
As well as this, marketplace content purchased on the Live account prior to the release of PS4 Bedrock do not transfer to PS4 Bedrock. In my case, the Faithful texture pack featured in the marketplace was purchased on my Live account (which I use with Windows 10 Edition and Pocket Edition) before PS4 Bedrock released. Once PS4 Bedrock was released, I signed into my Live account on PS4 Bedrock to find that the Faithful purchase was not transferred to PS4 and I would need to purchase Faithful a second time if I would like to use it on PS4 Bedrock.
 
A very similar bug, MCPE-58643, involves an issue in which Legacy PS4 Edition DLC packs fail to transfer to PS4 Bedrock. In contrast, this bug involves a different issue in which Legacy PS4 Edition DLC packs successfully transfer to PS4 Bedrock, but fail to transfer to other Bedrock platforms (ex. Windows 10 Edition, Pocket Edition) associated with the same Live account.