Windows 10 Update, Hickup With Flash Drives
We have read on-line that Microsoft’s May 2019 update might not happen for those with connected USB sticks or SD cards. Microsoft claims the update will simply not happen if the OS detects these connected devices. The reason, Microsoft might re-assign drive letters to those connected devices.

On my first pass of reading this, the reassignment of drive letters doesn’t sound all that bad. Especially for a removable drive. However; Microsoft goes on to state that internal hard drives could also be affected by the drive letter shuffle.
There is your red flag!
The newly published Windows 10 support document reveals; those computers already having the April 2018 (version 1803) or October 2018 (version 1809) updates installed will receive this error message: “This PC can’t be upgraded to Windows 10.”
The Microsoft documentation does not referrence internal hard drives getting reassigned drive letters when no USB or SD card is detected and for that reason we feel you are safe during the update process. This is why Microsoft is blocking the update all together when a USB or SD card is detected in your system. Microsoft understands the importance of mounted internal hard drives; thus their blocking of the update.
At the time of writing this, I had already seen 10+ articles about this problem from major technology and news outlets. With that said, it’s safe to say Microsoft will probably figure out a fix before the massive update rolls out.
For those of you who want to remove rogue registry entries from USB devices connected from the past, we’ve talked about USBScrub from Nexcopy. This is a registry cleaning tool for your Windows system and can speed things up when connecting USB devices. We say this because the longer list of reg entries Windows must sort through, the longer it could take to enumerate and mount that device. More info here on USBScrub.