This happens on both my desktop and my laptop.
There's an issue detecting USB installers on distros newer than 16.04 when using USB 3.0+ ports and USB 3.0 installation media.
It's related to the USB controller not detecting the live installation media even after successfully booting into the USB device from BIOS.
Regardless if the USB is plugged into a 2.0 or 3.0 port and whether or not the USB key is 2.0 or 3.0.
If your BIOS is unable to disable 3.0 USB support then you're out of luck except for the final workaround below.
Best Answer
Here's a set of potential fixes:
live splash
tonomodeset
Finally if none of those work, then you can try an answer I found after a ton of digging located here:
https://askubuntu.com/a/946334/85384
In essence, when it looks like Ubuntu is waiting for the USB stick to be present to read from you can unplug the USB stick and replug it back into the same slot. This fixed the issue for me 100%.