6X upgrade from 7.6.7.3 to 7.6.8.4 failed

[bigbangtech]

I updated our 6X from 7.6.7.3 to 7.6.8.4 using the web update. Update page showed "...Extracting Files" for quite a while. Phones lost registration, then came back up within a few minutes. Checked the about page, and it showed version was now 7.6.8.4. Phones automatically rebooted and loaded new software. After a few minutes more, phones lost registration again. Attempted to access the server at port 8080, no response. Physically looked at the server, and all of the FX port lights were lit amber. I gave it a good 20 minutes before I decided to power cycle the router, this time FX lights turned amber, and power light went from green to OFF. Power cycled, waited, no response, fx lights amber. Repeat.

Booted into safe mode and restored 7673 backup made just prior to upgrade, automatically rebooted, FX lights amber, power light off, no response.

Booted into safemode and restored 7673 backup from 2 days ago. This time, fx ports went from amber to off (normal), and I finally heard the relay click, and system came back.

All of the previous boot attempts, I never heard the relay click.

As a note, still have the original 256MB flash card with 47% free installed.

What could have caused all of these issues?