This is not an ordinary slide, so, you need to add the block differently from regular slides. There are two ways to add a Talking Head (Content block) in the storyboard.
1. Hover between the slides and click on the "Insert Talking Head" button
2. Or, click on "Insert Talking Head" from here
Not sure if you have access to this feature?
Check out what's included in your plan or contact our support.