I am also trying to use the latest ISO with the Preempt-RT kernel, and the installer fails at the "installing system" step. It also can't format the boot partition as vfat, because apparently the module to read and write FAT32 or FAT16 isn't included? I also have issues with the Realtek firmware for the NIC not being included either.
In order of appearance:
Need non-free firmware, rtl8106g-2.fw not included. I insert removable media (USB thumbdrive) with the realtek firmware .deb and the actual .fw file and it apparently can't access this, even when prompted. Leads to no network access during install.
During partitioning, I prefer seperate /, /tmp, /bin, and /home partitions, but I can work in anything that works. Unfortuntately, no matter what partitioning system I use, even the suggested systems, I get the same error during the installation step: Installing system failed. If I drop to a terminal and do a "cd / && ls" , I can see all the normal things I would expect, but if I try to mount sda0,1 at /, then cd to it and ls, I get what looks normal, but I have not done a comparison yet to see how much is missing.
Finally, if I just push it forward to install grub and try to boot a possibly crippled system, it fails to install grub and complains that it cannot access /boot due to not having the vfat module.
I've downloaded and verified the .iso and burned it with Rufus using both the .iso and dd methods, and I get consistently the same results.
System is a J3445 Celeron 1.5ghz with 4gb of ram and a 140gb Sandisk SSD.