Short description of issue
After refactoring our classic product card implementation to use Shopify Theme Blocks in a major theme update, existing merchant templates were migrated incorrectly during the upgrade process, resulting in empty product grids and broken product cards.
Reproduction steps
Have the old theme version installed
Update the theme to the new version through the Theme Store update flow
Open a collection page or homepage featured collection section
Product grids/cards render empty
Additional info
Because this was a major theme update, we expected Shopify to handle incompatible template structures differently during the upgrade.
The issue appears to happen because existing templates/*.json files from the previous theme version are migrated into the new version while still referencing outdated block structures that no longer exist after the update to Theme Blocks.
As a result, merchants are left with broken storefront sections after updating, without a straightforward way to repair them themselves through the Theme Editor.
Current workaround ismanually replacing affected template JSON files with the new default v7 versions or rolling back to the previous theme version
Questions:
Is there a recommended updating strategy for themes moving existing architectures to Theme Blocks?
How have other themes handled this?
Is there a way for major theme updates to replace incompatible templates?
Would Shopify consider fallback behavior?
What type of topic is this
Bug report