What causes this terrible situation?
Actually, the root reason is the change of the drive letter.
In response, Microsoft said it will fix the issue in the next rollup release.

According to study, there are a lot of issues that could affect the Windows 10 May Update.
USB bugs are one of the common reasons.
Recently, an increasing number of people find theirWindows update blocked.
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To figure this out, you should read the following content.
How Can You Recover Lost Files After Windows Update?
The new update is available to Windows Insiders.

The v1903 is still not perfect.
Actually, no system is perfect; so its not strange there will be problems.
MiniTool Partition Wizard is a wonderful tool to help you change USB drive letter Windows 10.

How to assign a drive letter Windows 10 with this tool?
How to change drive letter withCommand Prompt?
you’re able to also use the Command Prompt to change/assign drive letter in Windows.
It is true Windows 10 May 2019 Update may be blocked for anyone using USB or SD storage.
After reading the above content, you must know how to do when finding Windows update blocked.