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Since October 14, 2025—KB5066835 (OS Builds 26200.6899 and 26100.6899) update a 4 surface pro 9 devices which work for the business are unable to produce sound throuch casting to devices specifically Microsoft wireless display adapters.
Has this happened to anybody else?
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I found that changing the audio source a few times in succession fixes the issue
So it appears a service called mfd or similar is breaking on boot.
I am going to be testing with power saver mode disabled completely
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Here is the work around for the sound issue while casting without having to uninstall updates., until Microsoft releases new updates 🙂
Sound While Casting Fix:
this worked for us Came here to post this lol But also afterwards we were able to switch it off and continue with stereo sound
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Helpful workaround for me - I use MS screencasting in my classroom and was frustrated when audio no longer worked. This stopgap solution got me back in action! Looking forward to holistic fix in future update.
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Hello Jackson. We’re aware that after installing KB5066835 (OS Builds 26200.6899 and 26100.6899), some users have experienced issues with audio not passing through when casting to Microsoft Wireless Display Adapters. This behavior is currently under investigation by our engineering team.
In the meantime, you can work around the issue by rolling back the KB5066835 update or using Bluetooth or wired audio output until a fix is released. We expect this to be addressed in an upcoming cumulative update, and I recommend keeping Windows Update enabled to receive the latest patches as soon as they become available.
If this information helps clarify the situation or provides a workable solution, please click “Accept Answer” so others can find it helpful too 🙂
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If this is a known issue why isn't it on the known issues on the KB! I've just spent a while trying to diagnose this!
Dear Stevens.
The reason you don’t yet see this listed under the known issue section for KB is that our product and engineering teams are still in the process of validating the reports before publishing an official notice.
In the meantime, here’s how you can roll back the KB to restore your casting audio:
Go to Settings → Windows Update → Update history.
Scroll down and select Uninstall updates.
Locate KB in the list, select it, and click Uninstall.
Restart your device once the process completes.
Thanks and hope it will be usefull.
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We've had this issue as well, now affecting more and more devices (Surface Pros, various models). The workaround we've found is to change the audio to mono (instead of Stereo). It would be good to see this logged as a known issue (which it is!) and ETA as to when the fix might be available.
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We are having the same problem.
However we have two Win 11 25H2 devices which don't have this KB.
Any ideas or is there a sperate one for 25H2?
We have a device with 24H2 and it has the KB, we are just waiting for the user to come in so we can try and uninstall the KB.
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Can you post a link to the official Microsoft site that states this so I can watch for a solution? I cannot find a "known issues" reference to KB5066835 and this audio issue.
Thanks!
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Surface Laptop Studio here. Casting to a Miracast device (promethean board) stopped outputting audio after a recent windows update.
The weirdest part is how Spotify would refuse to play a song when casting & the audio is through the Wireless Cast Device. "Spotify can't play this right now". Buttons to interact with the song seem frozen due to the audio issue.
Thank you to the user above who mentioned the Mono audio fix - enabling this worked and audio goes through the casted device!
Hi Hailey,
Thanks for this information. I have reset my Surface Pro to see if that would resolve the problem. This problem still exists, but **KB5066835** does not show up in the list of updates to uninstall. Is there another way to remove this update?
Thanks!
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Good spot from James above, hitting windows typing mono and flipping it off Stereo works as a worka round. Must also be hardware dependant as our ASUS laptops not effected with same build and KB only Surface Pro's
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@HLBui Any idea when the updates will be ready?
Thank you, James! Switching "Settings-> Sound -> Mono audio" to "On" will get us by until this is fixed.
Flipping to Mono has worked a treat thank you.
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Switching to Digital Output for the sound AND selecting Mono made it work. Thanks!
We’ve also found that if we roll back the DolbyAPO SWC Device driver in device manager it resolves the issue and you can keep stereo. The driver in question was released some time ago so something new (like a windows update) has caused it to break.
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I have no option to roll back this driver unfortunately
same issue on a microsoft surface book 3. It started after installing the Preview Update (KB5067036) (26200.7019)