Power BI Dataflow "HelloWorld" Function Call Works in Preview but Fails on Refresh

[krmiller]

AI-assist on the post content.  🙂

Description:
I'm encountering a frustrating issue with Power BI Dataflows. I've created the absolute simplest function call to test refresh behavior. The function works perfectly in Power Query preview but fails when refreshing in Power BI Service.

Repro Steps:
I created two simple scripts:

Function Definition (fx_HelloWorld):

let
  fx_HelloWorld = (Hello as text) => true

in

  fx_HelloWorld

Function Call:

let

  Table = fx_HelloWorld("Hello World!")

in

  Table

Expected Behavior:

• The function should return true when called.
• Since it works in preview mode, it should also refresh successfully.

  Actual Behavior:

  • ✅ Preview mode works fine.
  • ❌ Refresh fails in Power BI Service with the following error:

    Error Details (From Refresh Logs):

    Error Details: We encountered an error during evaluation. Details: A localization error has been logged, it is safe to continue. Message: "Unknown evaluation error code: {errorCode}" Parameters: "104100" (Request ID: 6648b7de-4c53-4985-b75e-88f8c386e2e8)

    Troubleshooting Steps Taken:

    ✅ Verified that the function is defined correctly.
    ✅ Confirmed that there are no dependencies, external sources, or complex transformations.
    ✅ Simplified the function to the absolute minimum (=> true).
    ✅ Checked that it works inside the Power Query editor.
    ✅ Tested different parameter values—same result.

    Questions:

    1. Has anyone else encountered this issue?
    2. Is this a known bug in Power BI Dataflows?
    3. Any workarounds to force a successful refresh?

       Would appreciate any insights! 🚀

[v-mdharahman]

Hi @krmiller,

Could you please confirm if the issue has been resolved after raising a support case? If a solution has been found, it would be greatly appreciated if you could share your insights with the community. This would be helpful for other members who may encounter similar issues.

Thank you.

[v-mdharahman]

Hi @krmiller,

I wanted to check if you had the opportunity to review the information provided. Please feel free to contact us if you have any further questions. If my response has addressed your query, please accept it as a solution so that other community members can find it easily.

Thank you.

[v-mdharahman]

Hi @krmiller,

As we haven’t heard back from you, so just following up to our previous message. I'd like to confirm if you've successfully resolved this issue or if you need further help?

If yes, you are welcome to share your workaround and mark it as a solution so that other users can benefit as well. If you find a reply particularly helpful to you, you can also mark it as a solution.

If you still have any questions or need more support, please feel free to let us know. We are more than happy to continue to help you.
Thank you for your patience and look forward to hearing from you.

[krmiller]

Explicitly setting the return type didn't help.

I think the only recourse I have here is to file a bug.  In the meantime, I have abandoned this approach.  If Hello World doesn't work, this simply is not a path forward for me.

[v-mdharahman · Accepted solution]

Hi @krmiller,

If you are still unable to solve the issue or you think there is a bug then you can reach out to Support by raising a ticket with Microsoft Support.

Please refer below link on how to raise a contact support or support ticket.
How to create a Fabric and Power BI Support ticket - Power BI | Microsoft Learn

If I misunderstand your needs or you still have problems on it, please feel free to let us know.  

Best Regards,
Hammad.
Community Support Team

If this post helps then please mark it as a solution, so that other members find it more quickly.

Thank you.

[v-mdharahman]

Hi @krmiller,

We are following up once again regarding your query. Could you please confirm if the issue has been resolved through the support ticket with Microsoft?

If the issue has been resolved, we kindly request you to share the resolution or key insights here to help others in the community. If we don’t hear back, we’ll go ahead and close this thread.

Should you need further assistance in the future, we encourage you to reach out via the Microsoft Fabric Community Forum and create a new thread. We’ll be happy to help.

Thank you for your understanding and participation.

[v-mdharahman]

Hi @krmiller,

Thanks for reaching out to the Microsoft fabric community forum.

It looks like you are facing issues with refresh in your PowerBi Service when you are trying to refresh your dataflow. Try to specify the return type as "Logical" and redo the steps.

If you are still unable to solve the issue you can reach out to Support by raising a ticket with Microsoft Support.
Use the below link to raise a ticket with Microsoft support:

https://learn.microsoft.com/en-us/power-bi/support/create-support-ticket

If I misunderstand your needs or you still have problems on it, please feel free to let us know.  

Best Regards,
Hammad.
Community Support Team

If this post helps then please mark it as a solution, so that other members find it more quickly.

Thank you.

[krmiller]

I'm obviously trying to do something much more complex than the hello world above, but I just kept simplifying the query to try to root cause the issue until I arrived at the above, which I can't simplify any further.