Neither live CD nor USB image does boot in UEFI on my system. Black screen, that is all, no grub-efi does show up. So, not even coming close to the point to install or reinstall. With 18.04 UEFI ist fine and works as designed.
This is not a direct fix, but it is a way around the installation process.
Install ubuntu 18.04 as you said that it works
Make sure internet connection is working
Go to "Software and Updates" and then "Updates"
For "notify me for new ubuntu version", select, "Any new version"
Open terminal and type "sudo apt-get update"
Open "Software Updater", It will notify that a new verison 18.10 is available.
Download and install and there you go
Hope it helps