Did you try putting the USB into a different port? Early up in the thread you said you were not booting via the 3.0 port did you try to recently?
Also looking around on the Ubuntu forums and other Ubuntu hang out spots, it looks as if this issue only pertains ( or at least commonly ) to AMD computers. People were able to solve this problem by going into the bios and changing boot order to USB, HD, CD. Or by using a non-usb 3.0 port, and vice versa. And by booting via ahci mode if booting from a cd ( which you are not doing, but may want to try. )
Try another thumbdrive, port shouldn't matter since they should be backwards compatible with whatever. Disable secureboot if you're on uefi, also enable legacy mode. Maybe try 'slow formatting' it first if you're on windows, try 'cleaning' it with diskpart. Try another iso to usb writer, or if you're super unlucky you need to use a dvd or cd... that has happened.
Turned out to be the flash drive. I tried another drive and the installation worked just fine. It's strange, I've used that drive many times for other installs and never had a problem. Thank you everyone for the help, I really appreciate it!