Regression: Power BI miscalculates percentage for identical values under unchanged conditions

[catwilkerson]

Yes, I used Co-Pilot to report this because I tried so many DAX and etc ways to fix this and none of them have been working(shows the same issue) and this seemed like a clear way to explain it:

Description:

We’ve encountered a serious regression in Power BI that affects the accuracy of percentage calculations in visuals. This issue appeared suddenly around late September 2025 and impacts reports that have been live and stable for over a year.

Issue Summary:

We have a column (Column1) derived from SQL using a simple CASE statement:

sql

CASE WHEN [Label] = 'B' THEN 'B' ELSE 'A' END AS Column1

• The column contains only two values: "A" and "B". No blanks, no nulls.
• In a Power BI table visual, we display both "A" and "B" side by side using a measure that calculates percentage of total.
• Under identical conditions, "B" correctly shows 15%, while "A" incorrectly shows 100%.
• This behavior is new. The report has been live for over a year and previously showed "A" as 85%, which is correct.

What Changed:

• No changes were made to the report, data model, or SQL source.
• The issue appeared after a recent Power BI update.
• The same measure, same visual, same filters — yet "A" is now misbehaving.

Impact:

• This regression causes inaccurate reporting, undermining trust in Power BI dashboards.
• Stakeholders are questioning the reliability of the platform.
• We’ve already experienced multiple bugs in recent months, and this adds to growing concerns about platform stability.

Steps to Reproduce: However, important note, I would not be surprised if this only happens on legacy models.

• Create a table with a column containing only "A" and "B" values.
• Use a measure to calculate percentage of total.
• Display both "A" and "B" in a table visual.
• Observe that "B" shows correct percentage, while "A" shows 100%.

Expected Behavior:

• Both "A" and "B" should be calculated against the same total.
• "A" should show 85%, "B" should show 15%.

Actual Behavior:

"A" shows 100%, even when "B" is present in the same visual.

Environment:

• Power BI Desktop and Service
• Import mode
• SQL Server source
• No custom visuals or third-party extensions

TMDL Reference:

partition TableColumn1-3b8de688-e2b8-4f41-b39a-289c67f64674 = m mode: import source = let Source = Sql.Database("server", "database", [Query=" select *, concat(SID,Schoolyear) as SIDSY ,#(lf)case when [Label] = 'B' then 'B' else 'A' END AS Column1#(lf)FROM database.schema.table ", CreateNavigationProperties=false]) in Source

PS. The Support Ticket button is also not working or taking me anywhere to submit a ticket.

[catwilkerson]

We reached out to support and we able to resolve the issue. Thanks!

[v-tejrama]

Hi  @catwilkerson ,

Thank you @FBergamaschi  and @Jai-Rathinavel  for the response provided! 

Has your issue been resolved? If the response provided by the community member addressed your query, could you please confirm? It helps us ensure that the solutions provided are effective and beneficial for everyone.

Thank you for your understanding!

[FBergamaschi]

I tried to replicate the issue with a sample model, no anomaly

As was suggested, please try to go back to a previous version of PBI and check wjether the issue disappears, if yes, I would raise a ticket to Microsoft

Another point could be that your code is delicate and now it broke, so please paste here your code

Mine was

If this helped, please consider giving kudos and mark as a solution

@me in replies or I'll lose your thread

Want to check your DAX skills? Answer my biweekly DAX challenges on the kubisco Linkedin page

Consider voting this Power BI idea

Francesco Bergamaschi

MBA, M.Eng, M.Econ, Professor of BI

[Jai-Rathinavel · Accepted solution]

@catwilkerson

Have you checked the percentage in a previous version of Power BI Desktop? Since you mentioned that no changes were made on your end, it might potentially be a bug. Please reach out to your platform admin to raise a support ticket  in my case, the Microsoft team called within 24 hours.

In the meantime, if you’d like to fix this issue quickly, let’s revisit your measure calculation. Could you confirm whether your percentage measure is using the following logic?

Percentage = DIVIDE(SUM('Table'[Value]),CALCULATE(SUM('Table'[Value]),ALL('Table')))

 Thanks,
Jai