WPF window render freezing on windows 11 update 25H2

Question

Hello.

Our client is reporting worrying problems that started happening after updating windows 11 to version 25H2 (it is possible it was also happening with 24H2, not sure at this moment), but it is definetly not happening in 22H2. Everything else is the same.

The problem is that the rendering for windows application written in WPF XAML simply freezes in one of the core DLL functions. Unfortunately it's hard to replicate it since it does not happen on our end.

It seems to be happening in SyncFlush function of Windows Media Composition somewhere in WPF.

It looks like a function that is responsible for drawing the window, and there is little we can do to affect it. We tried turning hardware acceleration to off but it did not help.

Has anyone seens something similar?

Answer 1

It appears that the freezing issue you are experiencing with WPF applications after updating to Windows 11 version 25H2 may be related to render thread failures, particularly in the SyncFlush function of the Windows Media Composition. Such issues can arise from various causes, including problems with video hardware or drivers, as well as potential bugs in WPF itself when interacting with the graphics hardware.

Since you have already tried disabling hardware acceleration without success, here are some additional recommendations that may help diagnose or mitigate the problem:

1. Update Video Drivers: Ensure that the video drivers on the affected machines are up to date, as outdated or incompatible drivers can lead to rendering issues.
2. Monitor Resource Usage: Use Performance Monitor to track memory usage and other resource metrics to identify if the application is exhausting any resources, which could lead to System.OutOfMemoryException errors.
3. Test on Different Hardware: If possible, test the application on different hardware configurations to see if the issue persists, which could help isolate whether it's a hardware-specific problem.
4. Check for Known Issues: Review the release notes for Windows updates to see if there are any known issues related to WPF or rendering that have been documented.
5. Collect Detailed Information: If the issue is reproducible, gather detailed information such as call stacks, crash dumps, and a description of the environment to assist in diagnosing the problem further.

Since the issue does not occur on version 22H2, it may be worth reporting this to Microsoft if it continues to be a problem, as it could indicate a regression or compatibility issue introduced in the newer versions.

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References:

• Troubleshoot WPF render thread failures
• Resolved issues in Windows 11, version 25H2

Answer 2

Thank you for reaching out.

This behavior matches a known WPF render thread issue described by Microsoft.

The freeze you see in SyncFlush does not mean your code or controls are stuck. In WPF, drawing is done on a separate internal render thread. When something goes wrong inside the Windows graphics stack (DirectX, DWM, or related OS components), WPF reports it later at points like SyncFlush, even though the real failure already happened earlier and is lost.

This explains why:

• The app works on Windows 11 22H2
• The issue appears after upgrading to 24H2 / 25H2
• It happens on multiple machines, different vendors and GPUs
• It cannot be reproduced on your machines
• Disabling hardware acceleration does not reliably help

Microsoft confirms these render thread hangs are generic symptoms, not a diagnosable app error, and there is no single code fix. Controls like RichTextBox, TreeView, or Telerik controls are not broken they just increase rendering activity and can expose an underlying WPF/Windows issue introduced in newer OS versions.

In short, this points to a Windows / WPF platform regression, not an application or third‑party control issue. There are only mitigations (like reducing visual complexity), but no reliable application‑level workaround.

Reference:
Troubleshoot WPF render thread failures https://learn.microsoft.com/troubleshoot/developer/dotnet/framework/general/wpf-render-thread-failures

Please let us know if you require any further assistance, we’re happy to help. If you found this information useful, kindly mark this as "Accept Answer".