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I had this message myself; I am in the Release Preview Channel of Windows 11 25h2.
But I found a solution that works: Changing the update channel for Windows Defender only.
It is possible that your current update channel is in the beta channel, which is why Microsoft Defender is currently "maybe" finding an error in the hash of a file. You can check this in your Windows event viewer.
You can manually adjust the update channel to the Current Channel (Staged) of Windows Defender.
PowerShell:
Set-MpPreference -EngineUpdatesChannel Staged
Set-MpPreference -PlatformUpdatesChannel Staged
Set-MpPreference -DefinitionUpdatesChannel Staged
Then in cmd:
cd "C:\Program Files\Windows Defender"
MpCmdRun.exe -ResetPlatform
Finally, check for new updates/definition updates in Windows
You are now in Current Channel (Staged) instead of Beta Channel in Microsoft Defender.
This worked for me. It might be worth a try; you can find information about this on the internet.
