Matrix visual column width rendering regression in Power BI Service

Hi tt_and, 
Thank you for reaching out to the Microsoft Fabric Community Forum.

Based on your description, this behaviour appears to be related to how Matrix visuals handle column sizing in Power BI Service. As per Microsoft documentation, Matrix columns can automatically adjust their width depending on content and layout settings (such as auto-size or fit-to-width behaviour), which can override previously applied manual resizing especially when a column is resized smaller than its content.

As a workaround, please try disabling Auto-size column width in the Matrix formatting pane and then manually resizing the columns again. Microsoft also notes that fixed column widths are not strictly enforced in all scenarios, so manual adjustments may be impacted by visual layout behaviour.

You can review the following official documentation for more details:
1. Matrix visual format settings: https://learn.microsoft.com/en-us/power-bi/visuals/power-bi-visualization-matrix-visual-format-settings 
2. Create a Matrix visual in Power BI: https://learn.microsoft.com/en-us/power-bi/visuals/power-bi-visualization-matrix-visual 
3. Matrix visual considerations and limitations: https://learn.microsoft.com/en-us/power-bi/visuals/power-bi-visualization-matrix-visual-considerations 

If the issue started recently without any report changes, it may be due to a change in how the service applies these layout behaviours. Reapplying the layout from Power BI Desktop and republishing can also help ensure consistent rendering.

Hope that clarifies. Let us know if you have any doubts regarding this. We will be happy to help.

Thank you for using the Microsoft Fabric Community Forum.