Comment 3 for bug 1788659

This is working as designed.

NetworkManager now uses a metric "penalty" when connectivity cannot be detected as full for a connection, and reduces the metric accordingly.

This makes it so that if you're connected to both wired and wireless, and your wired connection becomes bad but the wireless connection remains, you should retain connectivity.

Similarly, if you need to use your own custom routes to use alternative paths to be online, this makes sure this alternative can be used automatically (the lowest metric is what gets used).

You may be able to avoid this issue by removing package 'network-manager-config-connectivity-ubuntu' from your system if it is installed -- disabling connectivity checking, which will avoid going through these code paths.