Just found this link to update file directly via ASUShttps://dlcdnets.asus.com/pub/ASUS/ZenFone/ZS630KL/UL-ASUS_I01WD-ASUS-18.0610.2101.127-1.1.1-user.zi...
Downloaded and updated manually yesterday and everything works out fine. Have no issues so far.
Just download the file, copy it from download directory into the root directory of the phone (via Filemanager) and restart the phone.
Update file will be detected automatically and is now ready to be installed.
Disclaimer: use on your own risk