Unable to Load The Panel Source

Here we go.

Sunday, September 15th, 2019. Upon loading the home assistant UI, I receive an annoying javascript popup error:

An embedded page on this page says
Unable to load the panel source: /api/hassio/app/entrypoint.js.

Opened developer console in Chrome to investigate and found the following:
Found multiple references to custom-panel.ts. Investigating further.
SSH into HASS.io on Ubuntu server and ran hassio ha check. Met with the following message:
Post http://hassio/homeassistant/check: dial tcp 172.30.32.2:80: connect: no route to host

Okay, so we have a potential network issue between docker and Ubuntu.
Attempted hassio ha restart only to see the same no route message. Not sure what it means.
SSH into Ubuntu and check docker: systemctl status docker. Incidentally, I can't stop typing cocker by mistake. Result is a list of running docker containers.
sudo apt-get update && sudo apt-get upgrade
Checked docker status, none of the containers appear to be running. Still have limited experience and understanding of Docker.
Rebooted Ubuntu server.
After some time, Home Assistant came back online, but with a few problems, including some Ingress errors, likely due to a change in port numbers on containers and a firewall that's blocking those new ports.
Added both offending ports to FirewallD.
Add-ons that weren't loading due to 502 Bad Gateway are now loading without fail.

It appears the problem has been solved.