In case you are still experiencing difficulties with updating GOG GALAXY please get in touch directly with our GOG GALAXY Team regarding the problem:
Top left corner cogwheel in GOG GALAXY -> Report issue

If for some reason you can't get to GOG GALAXY, please use the following form.

Please attach a zipped logs folder to your report.

To get to your logs folder use the Run command (WinKey+R key combination) and enter:
%programdata%\GOG.com\GALAXY\Logs

As a workaround, you could try to force launch the update once again by using the web installer.