Upgrade block list for Windows 10 May 2019 Update (19H1)

Windows 10 May 2019 Update will be made available in late May for commercial customers on a currently supported version of Windows 10 who seek to update via “Download and install now (”limited to devices with no known compatibility issues). A phased rollout using ML model* will start to intelligently target those devices running Windows 10, version 1803 or prior versions that Microsoft’s data and feedback predict will have the best update experience.

Upgrade blocks for the May 2019 Update (19H1) :

Recently Microsoft has released a list of Upgrade Blocks for the May 2019 Update. So one must be aware if he’s having any issues when this update is made available.

• If you have an external USB device or SD memory card is attached to your PC, you will be blocked from updating to the May 2019 Update. If you remove any external USB devices and/or SD memory cards, the update should proceed normally. This issue will be resolved in a future servicing update for Windows 10. For Windows Insiders, this issue is resolved in Build 18877 and later builds.

Windows Insiders who are trying to upgrade to the May 2019 Update may experience an upgrade block and receive the following error:

"This PC can't be upgraded to Windows 10"

Example: An upgrade to the May 2019 Update is tried on a computer that has a thumb drive inserted into a USB port. Before the upgrade, the device would have been mounted in the system as drive G based on the existing drive configuration. However, after the upgrade, the device is reassigned a different drive letter. For example, the drive is reassigned as drive H.

Note The drive reassignment is not limited to removable drives. Internal hard drives can also be affected.

Workaround: To work around this issue, remove all external media, such as USB devices and SD cards, from the computer. Then, restart the May 2019 Update installation

• If you have older versions of anti-cheat software used with games installed on your PC, you will be blocked from updating to the May 2019 Update. Some older versions of anti-cheat software may cause PCs to experience crashes after updating to the May 2019 Update. This block is specific to older versions of anti-cheat software. Microsoft is working with partners on getting their software updated with a fix, and most games have released patches to prevent PCs from experiencing this issue. To minimize the chance of hitting this block, please make sure you are running the latest version of your games before attempting to update the operating system.
• If you have redirected any Known Folders (for example: Desktop, Documents, Pictures), an empty folder with that same name is created in your %userprofile% directory when you update. Your Known Folders are redirected if you chose to back up your content to OneDrive using the OneDrive wizard, or if you chose to keep your content backed up during the Windows Out-of-box-Experience (OOBE). You may have also redirected your Known Folders manually through the Properties Dialog in File Explorer. ​This issue does not cause any user files to be deleted and a fix is in progress.

So keep these upgrade blocks in mind before installing Windows 10 May 2019 update

(source)

*(check this for more details on Next generation of ML-based intelligent rollout)