I could not create a bug report, so I publish the failure when ISO-testing here.
Toshiba Satellite C850-19W booted in UEFI mode. Tried to install using the whole drive using Swedish, get updates and encryption (on a drive that was encrypted).
It failed 
“Bad main script file. Details: Main script file /usr/lib/x86_64-linux-gnu/calamares/modules/unpackfs/main.py for python job unpackfs raised an exception.”
I could not run ‘ubuntu-bug’ after this failure. I could not even run the text screens (they were filled with SQUASHFS errors), so there is no bug report. I suspect that it fails to get updates, will try without that (but still with Swedish and encryption) …
Yes, without trying to get updates, the installer finishes as expected. After reboot the installed system booted and offered upgrading, which finished successfully. So there was ‘only’ a problem when calamares tried to upgrade.
We should either check/fix this or remove the option from Calamares “Additional Options - Download and install updates following installation”
