It could read the data just fine booting from another drive. Even a reinstall on the SSD didn't fix the broken booting. I had to repartition, then it worked just fine.

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Migrating a Windows installation can be tricky. Thankfully, our guide will show you how to move Windows 10 to an SSD from your dusty old hard drive in no time.

The simplest way to upgrade from a smaller SSD (or HDD) to a larger one is to pull the old drive, install your new drive, and then install your version of Windows from scratch onto the empty drive.