This error occurs when a GroupRule returns an unexpected result shape from execution (for example, missing expected fields or returning a non-boolean/non-result type where a result is required).
Example Trigger
This is most often caused by a custom rule implementation returning an invalid value.
Solution
Ensure custom/group rule implementations return the expected validation result type.
If a rule is async, return a Promise that resolves to a valid result.
Troubleshooting
Log the value returned by the failing rule to see what is being produced.
Review custom rules for correct return types and error handling.
