Hardware issues, errors with the update itself, and pending updates are common causes of upgrade assistant getting stuck halfway through an installation process. These are three very common scenarios associated with a stuck Windows 10 Upgrade problem.
This problem reveals itself in multiple ways.
You may still need to upgrade Windows 10 service packs and drivers to completely download and install the upgrade. During the process of upgrading your Windows 10 did the upgrade get stuck at 99%? If it did, it doesn't mean that Upgrade Assistant is no longer functioning.
