When you have a content with empty field blocks (blocks={}) and empty field blocks_layout (blocks_layout={items:[]}), for example because it comes from a migration, or is a content generated automatically by Plone, when you put text inside first text block and save, only blocks field is saved and blocks_layout is still empty.
This then brokens the view.

To Reproduce
Steps to reproduce the behavior:

1. Create a new page
2. Save it
3. Go on Plone and edit the page created setting field 'Blocks' = {} and field 'Blocks layout' to {items:[]}
4. Return to volto and enter in the edit mode of the page
5. put some text into text block
6. save
7. Go to plone, you will see that Blocks layout is empty and the view of the page in Volto doesn't show anything!