Personal Comments:
I’ve been file-looping since SU4, and am on Steam Version. How I got WU6 to install is pausing the installer after each time I detected the file looping happening and exiting. Then I start the sim/installer again.
The third time, it detected that the simultaneous download while decompressing 2.6GB wasn’t working and reverted me back to Version 1.16.x.x. While unfortunately that jumped the update from 2.6GB to 15.6GB, I was able to finally successfully complete the update. Hope this works for you.