What is the Acquia Cohesion hidden region?
The Acquia Cohesion hidden region is a useful holder for blocks that you want to render using the Acquia Cohesion block element.
If you want to place Drupal blocks in your layouts using the 'Block element', your block needs to first be placed within a region within Structure > Block layout. Once a Block has been placed, it becomes available to the Block element.
The Acquia Cohesion hidden region is a useful holder for blocks placed using the Block element as the region does not render to the front-end of your website.