I know this thread is a couple years old, I've experienced this too. The issue appears to be a question of how the WAN ports are being configured. The MX units ports can be configured through the Dashboard, but it will not stick or it will lie about a config. My most recent experience is that our WAN1 port had to be configured with a Vlan ID tag for the traffic to reach the other side. In the Dashboard, the tag was setup correctly. When I consoled in, the tag was missing. So, going forward, all new configuration changes to the MX WAN ports will have to be done through the console port, on site.
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