eth1 (WAN) disappeared?

This is a weird one...

Last night, I configured my ERL (running EdgeOS 1.8.0) for ipv6 following this guide. 

I noticed tonight that it wasn't working, so as a first (lazy) troubleshooting step, I rebooted the device. And when it came back up, I found that eth1 (my WAN port) is no longer showing in the UI:



If I run 'show interfaces' on the command line, I get this:

myuser@hostname:~$ show interfaces
Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface    IP Address                        S/L  Description                 
---------    ----------                        ---  -----------                 
eth0         [my subnet]/24                      u/u  Local                       
eth1         [my external]/21                   u/u                              
eth2         192.168.2.1/24                    A/D  Local 2                     
lo           127.0.0.1/8                       u/u                              
             ::1/128                          

And in config mode, I get this:

myuser@hostname# show interfaces
 ethernet eth0 {
     address [my subnet]/24
     description Local
     duplex auto
     ipv6 {
         dup-addr-detect-transmits 1
         router-advert {
             cur-hop-limit 64
             link-mtu 0
             managed-flag false
             max-interval 600
             other-config-flag false
             prefix ::/64 {
                 autonomous-flag true
                 on-link-flag true
                 valid-lifetime 2592000
             }
             reachable-time 0
             retrans-timer 0
             send-advert true
         }
     }
     speed auto
 }
 ethernet eth2 {
     address 192.168.2.1/24
     description "Local 2"
     disable
     duplex auto
     speed auto
 }
 loopback lo {
 }
[edit]

However, it is definitely passing traffic - the external interface is running, has an IP address, routing is working, etc.

Any idea what's going on here? I have a backup of my old config that I can try loading, but I'd like to understand what the root cause is. (And eventually figure out why my ipv6 stopped working, but that's the next step....)