SOLVED
The solution: Deleting the following files prompted the launcher to redo the update. It had it download >50GB but at least it solved the issue entirely. Maybe it was just one corrupt patch file and that deleting just that single file could have fixed it (and perhaps made the subsequent download much smaller?).

I've tried multiple times now, the installer stops at 18389.36MB (30%) every time I try to run it. On top of that Windows seems to run slower in some functions (like opening task manager takes 5 seconds instead of instantly for example, starting my otherwise leightweight screenshot program Greenshot takes 10 seconds instead of instantly and saving the screenshot image file takes another 10 seconds instead of saving instantly. File/folder browsing is laggy as if there is a lot of disk usage happening... from the launcher perhaps? then what disk usage is it doing if there is no progress?), yet other programs and functions work as fast as always (for example opening my browser and typing this text).
I've tried restarting Windows. Tried disabling and closing my antivirus, firewall malware programs. Tried waiting >50 minutes. But didn't help, launcher still stops updating at exactly 18389.36MB. What is going on here.... I can't bear to make a complete redownload and reinstall


Interestingly disk usage is 100% so the launcher must be doing something to/on my harddisk...? what is it and how can I fix it?
Edited by Jayman1000 on October 24, 2017 7:03AM