Thanks for your reply and patience.
Just to make sure, I did check the sha256sum, and it's ok.
I tried to edit the system-boot page by appending the kernel like as you suggested, but the problem persisted. Just in case, here's the list of available KaOS options, followed by a brief description of what I did.
KaOS_2018.06 GNU/Linux, with Linux kernel
KaOS_2018.06 GNU/Linux, with Linux fallback kernel
EFI Default Loader
Reboot Into Firmware Interface
I selected to edit the first option by using the 'e' key. Entering the 'enter' key after that booted the system right away as before, so I restarted the computer and skipped this second step ('enter' key) by adding "3" at the end of the kernel line on the bottom of the screen so that the line ended in 'rw3'. Then I pressed 'enter' which booted the KaOS but again froze after the login, right at the Plasma loading screen.
Just to make sure I also decided to reinstall the OS. I used the automatic partitioning option (erase entire disk) as before. This time I did notice two additional small partitions (displayed in grey color) before and after the main three partitions selected by default.
I know you mentioned that automatic partitioning may not work with UEFI, but perhaps if I attempt to reinstall KaOS once again, this time manually partitioning the disk in order to avoid additional partitions being added, could help in the end?