Dug out my ER-X-SFP to upgrade to 1.8.5 and the device has bricked itself! 
Following the upgrade, the device stops functioning and is not reachable on the network.
Full dump of the boot process from serial console here (normal-startup.txt):
https://gist.github.com/dowlingw/8fa9cd5b3ba312e297c3cb14a17a568f
It looks like the configuration file/partition is corrupt and it's not receiving any configuration.
Here are some observations from troubleshooting:
- No matter what reset method used, same results
Output on console:
[....] Starting EdgeOS router: migrate rl-system configure failed!
- Default (and known) username and passwords not working
- No ARP or IP traffic observed from the device
- Only the backup image works (see link above)
Looking at the console output, it's unclear whether the cause is a corrupt configuration, the configuration partition itself or something else causing the issue.
https://wiki.openwrt.org/toh/ubiquiti/ubiquiti_edgerouter_x_er-x_ka
I'm going to try TFTP booting a different image to see if I can flash from that but wanted to check to see if anyone else has had this issue or knows how to lay down a fresh/blank config.
Cheers 