Can you get a copy of the execution report and attach it here (after sanitizing it of course)? Exit the workflow, click on its name, switch to the Executions tab in the right side popup, and download the execution report for your latest run. I can explain this better if needed. Even for tests and not actual runs, the execution report should still be available and might have some more information to help troubleshoot this issue.
Example:
Thank you,
- Zach