HomeAssistant is externally accessible through DNS but supervisor does not load

I recently setup HomeAssistant to be externally accessible using DuckDNS and let’s encrypt. I’ve got that working except for the supervisor. As can be seen in the attached image, the supervisor is just a blank screen. Everything else works, except ESPHome which also displays a dark screen. I left it to load for a while and nothing happened. Any ideas why this would happen? I’ve tried rebooting multiple times and it hasn’t helped. Running it on a Pi 3B if that makes a difference.

Also it worked perfectly before I made it externally accessible, which is strange

Cleared browser cache?

Just tried that and unfortunately supervisor is still a blank dark screen