I suggest you read this document:
At the end of page one, there's a button to contact support.
There are some known compatibility issues with some MAC, and apparently with some Lenovos too (T470 I heard).
If you have a docking station, try without, I had issues on my T480s with docking, once I removed it (and added a simple usb hub to have 2 more usb ports on the laptop), it worked properly.
I had the same problem, what I found is that I could not simply change the boot order to have the USB boot first. I actually had to select the usb disk in the bios menu and say boot from there. I really hope this helps you, I had the same problem.
Or if you still have the old iso you can use that, I sat an exam last Friday with a USB from June 2020.
As I mentioned in my previous post, this was very difficult and there were no instructions. All I thought I had to do was create the bootable usb and change the boot order in bios or uefi. NOPE, you have to actually boot from bios to the usb, I had to select the boot menu and then click the usb to boot immediately from the usb. Again you cannot just change your boot order to boot from usb first, you actually have to boot from the usb while you are in bios. I did this on two separate computers and it worked. You have to find the boot menu ( not the boot order menu) the click on the usb and boot immediately from that device no F10 Save and exit, you have to boot immediately from bios. I hope this helps you, it is not documented anywhere and I got the complete "Run Around" when I opened a ticket.