I have tried installing 11.2 on two seperate flash drives, one of them managed to boot. But I'd like to install FreeNAS on the SSD I have in the machine, and keep my flash drive.. I have wiped and reinstalled the SSD multiple times by now, and have also tried installing the OS to the SSD by using an external USB-SATA connector and installing FreeNAS in a VirtualBox instance to the SSD directly. This didn't boot the OS either.
At first I tried updating from 11.1U6, since that was the installed version on the system. When this wasn't working, I installed the 11.1U7 update to see if I could then update to 11.2, but unfortunately this didn't work.