Hi,
I just thought of something concerning your USB drive...
Did you ever turn the Legacy USB Support back on ?
Also... You might need to change the 1st Boot Device in your Bios to the SSD..
You should be able to set the Flash Drive as the 1st boot device and not cause any problem... Unless the USB drive has something on it that makes your Bios think it is bootable...
The best thing at the moment would be just make the SSD the 1st device, and use the BOOT OPTIONS menu if you need to boot with the flash drive...
If you still have problem, you can run sfc /scannow to check system files...
Here is a good article if you continue to have issues concerning Restoring Health of Windows 10... The very end of the article is important...
https://www.windowscentral.com/how-use-dism-command-line-utility-repair-windows-10-image