I've had better luck from the Safe Mode because I evidently have some 3rd party software that interferes with the installation so try the following:
#1 - boot into Safe Mode according to Start up your Mac in safe mode - Apple Support.
NOTE: Safe Mode boot can take up to 3-5 minutes as it's doing the following;
• Verifies your startup disk and attempts to repair directory issues, if needed
• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)
• Prevents Startup Items and Login Items from opening automatically
• Disables user-installed fonts
• Deletes font caches, kernel cache, and other system cache files
NOTE 2: If you have a wireless keyboard with rechargeable batteries you should connect it with its charging cable to assure a boot into Safe Mode or the Recovery volume.
#2 - go to the System/Software Update preference pane and begin the download.
#3 - run the installer from the Safe Mode.