@Edward
So you have a Jessie image? In case could you please try:
sed -i '/[[:blank:]]Workaround_WiFi$/a\\t\tsystemctl start networking' /DietPi/dietpi/boot
There is a current bug on Jessie that prevents networking service to be started on boot. The above adds a manual service start to DietPi boot script.
But you mentioned that the update breaks in the middle. Please paste the error messages that you see on terminal, as this should not be related.
@sessho
Could you please file a bug report on GitHub about this? Seems to be a separate issue, perhaps due to recent feature to add multiple WiFi SSIDs: https://github.com/Fourdee/DietPi/issues