Behavior:

• Create a new Page.
• Add an "Hero block"
• Preview in Edit mode
• Send for publish later
• Reedit draft before that later date

Experienced behavior:

• when I reedit the draft, the preview of the Hero block created doesn't show any content.
• if I edit the block, the selected content info is still there
• if I re-save the block, I generate an error.

Expected behavior:

• Hero block should be available for Preview in Edit mode as when I first
  created the draft.

To reproduce, watch the sequence, see screencapture attached.

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Simplified flow below.

Summary: Cannot generate block preview when draft exists but published version doesn't.

Steps:

1. Create new empty Landing Page.
2. Fill Title and Description.
3. Save draft.
4. Add a block e.g. Embed.
5. Open settings and select content e.g. article.
6. Submit.

Actual result: Preview is not generated, error occurs in UI "Cannot update blocks preview" (console error attached).
Expected result: Preview is generated.