Error occurs when adding content item to Schedule block with "circular" overflow set.

Steps:
1. Create a new Lading Page with 3 zones.
2. Add a Schedule block to each zone.
3. Set templates to hero, list and grid. Customise the names of the blocks.
4. Set overflow from zone 1 to 2, from 2 to 3 and from 3 to 1 ("circular").
5. Add a content item to the Schedule block in zone 1 (e.g. blog post).
Issue: Block preview is not generated, error "Error occured when getting block preview" occurs.