I'm not with Laminar Research, just a fellow simmer in the UK, but having looked at your X-Plane 11 log file, I can see that it is absolutely full of errors about reading DVD 4 and also many reports of corrupt files.
Your post seems to suggest that you are downloading the 'demo' version from the LR website via their Installer app, but this seems at odds with the DVD 4 references in the log file??
Your log file also has many references similar to this one:- The downloaded file has corrupt contents (C:\jenkins\design-triggered\source_code\app\Installer-f\ins_tasks.cpp:822)!
I have seem this reference to 'Jenkins' many times before in other simmers posts, but have no idea what it means, nor does anyone else it appears? Personally I have never come across this in any of my own log files!
When you use the X-Plane Installer, are you doing this through the X-Plane 11 application itself, or through the standalone X-Plane Installer app? Do you have an X-Plane DVD in the PC at the same time you are trying to update?
Do you have any anti-virus software on your PC that could be preventing the install download?