Summary
Two protected workflows (ParentWF and ChildWF) live on the same git feature branch, where ParentWF triggers ChildWF inside a loop block. Since last week, that loop fails on every iteration with an 'Internal server error' / '"undefined" is not valid JSON', ChildWF never shows any runs in Run History, and the failure only occurs once ChildWF is moved onto the feature branch (both on main works fine).
AI Response
This pattern of symptoms points to a source-control state issue on the feature-branch copy of the workflow rather than a problem with the block logic itself. A closely matching community report shows a protected workflow that consistently returns 'Internal server error' only on a specific branch, works fine on other branches, and shows no workflow runs on the affected branch — and Retool staff identified the likely cause as the source-control state of the workflow as a whole. The suggested next step there was to create a fresh branch and re-check out the workflow, since the corrupted branch state persists even after switching the child back to main. It's also worth confirming, per the Run Workflow block docs, that ChildWF contains a Response block and is referenced/deployed correctly, as a child run behaves like a webhook-triggered workflow and must return data to the parent. Recreating the feature branch is the most consistent workaround reported for this branch-scoped internal error.
Sources
Retool Workflow just shows 'Internal Server Error' for everything and anything on specific branch
A near-identical report of a protected workflow returning 'Internal server error' only on one source-control branch (works on others, no runs recorded), where staff attributed it to the workflow's source-control state and suggested creating a new branch.
Documents how the Workflow block runs a child workflow like a webhook-triggered run and requires a Response block to return data, useful for verifying ChildWF is configured to return correctly.
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