I believe that I am also experiencing this issue. It happened to me today while moving some stuff around someone pulled the ethernet cable out by mistake.
After the ethernet link was reconnected and the internet connection didn't come back up, I logged into the routers GUI. As best I can remember the pppoe interface showed as connected and had some activity in the dashboard (a few kbps) but the internet connection wasn't working. I started a config backup and the GUI became unresponsive a little while after and I was no longer able to load the GUI. I pulled the power and plugged the ER-X back in and we were back in business. I guess it's possible that my issue is not the same since I was doing a config backup at the same time but it sounds similar enough.
This is on v1.9.0. The router is otherwise pretty stable with around 10TB a month flowing through it. I'm not running any VLANs but as far as I understand the network topology beyond the router pppoe is running on a VLAN. No OSPF or MPLS going on either.
If there is anything I can provide that might help let me know, along with how I can provide it. I'd be happy to help figure out what's causing this.
