Comment 7 for bug 1522261

We also met the same issue on OTA image upgrade in Beijing office before, because of the network connectivity in Beijing office is not very stable sometimes, so not very sure if it's related with the bad connectivity in Beijing, but seems the OTA image upgrade issue is worse recently if there is a bigger size of image updates to be upgraded,

In the very beginning, OTA image upgrade works no matter with/without VPN network,

For now, OTA upgrade works only with the VPN network and the image updates size have to be less than 10MB around, but sometimes also need to try more times. If with the non-VPN network, the downloading process goes to 100% directly, then get the popup "Installation failed"
If the image updates size is bigger than 10MB (like upgrade for crossing many builds), it's hard to success even though with the VPN network, the downloading will be interrupted easily.

Found some abnormal lines in logs of application-legacy-ubuntu-system-settings-.log and ubuntu-push-client.log, hope that could help.