Using blocks in TinyMCE editor (epi-contentfragment)

Hi all,

We're busy migrating multiple websites from CMS 11 to CMS 12 and one thing we're stuck on is drag-and-dropping blocks in TinyMCE editors. On the CMS 11 version this renders the block fine:

But on CMS 12 it just renders the title:

<div class="epi-contentfragment">Advertorial block banner div 1</div>

When debugging, it seems like the code runs through the BlockComponent and View, but somehow I guess it gets changed to the div above.

This happens to blocks that have a dedicated BlockComponent but also blocks using the DefaultBlockComponent.

Is there anything you need to enable for this to work between v11 and v12?