Hi Grif,
You should know that when a post was previously created using other composers, it is not possible to switch the composer used initially to other composers while editing back that same post. In other words, when editing a post, the composer loaded will always be the composer that was first used to create the post. For example, if you use TinyMCE to create post A, while editing post A in the future TinyMCE will always be loaded, regardless of what default composer is chosen at the time.
This is because the system is not capable to adapting the post to a different composer as each composer has different sets of functionalities that may not be carried over to another composer.
I have check your backend settings: Settings>General>Composer>Composer Settings>Composer Editor. This is set to TinyMCE. I have changed that to EasyBlog built-in composer. In the future, when creating new posts you will now be able to use blocks.