Octoprint doesn't run anymore :(

What is the problem?
"The OctoPrint server is currently not running."
I just cannot connect to it anymore. No SSH, no octoprint.local, remote access isn't possible anymore. I've currently hooked up the SD in a different Pi with a connected monitor, mouse & keyboard for easier access and it does boot normally, and I can interact via command line. When checking with "sudo service octoprint status", it says active. But it obviously isn't active.

What did you already try to solve it?
The Pi was initially connected via WiFi, but is now connected via Ethernet, just to make sure, that's not the issue. Also tried the SD on a separate Pi.

I've also burned a new OctoPrint version on a separate SD, which works fine, but lacks all of the settings. If I could figure out, how to move over the settings to the new version, I'd be fine with just formating the old SD and scrap that thing without further troubleshooting. But I can't seem to connect properly to do that. Definitely gonna keep a backup in the future.
Logs (syslog, dmesg, ... no logs, no support)
Logs: (the dates are all messed up. I don't know if its correct or not. Had given up on octoprint for many month and only tried again today. OctoLogs.zip (101.0 KB)

Additional information about your network (Hardware you are trying to connect to, hardware you are trying to connect from, router, access point, used operating systems, ...)
I have Ubuntu 20.10 PC, Windows 11 PC, Windows 10 Laptop, Android 9 smartphone and the issue is the same for all, when trying to access OctoPrint.
The network consists of 1 WiFi router Speedport Smart 3. No access points.
OctoPrint initially ran on a Pi 3 via Wifi, though now for testing, it's running on a Pi 2 via Ethernet.