For more than a month I was trying to get an old Windows Server 2012 R2 VM running on fully patched Windows Server 2025 with Hyper-V. In September 2025 I needed to speed up this process so I was searching the internet for a possible solution. In fact something has changed (and deployed via Windows Update) on Windows Server 2025 and/or Hyper-V that causes this problem – I have also went through this thread but adding new SCSI controller did not help..

After removing (in September 2025) update KB5063878 Windows Server 2012 R2 VM booted without problems: