Help me: The OctoPrint server is currently not running

What is the problem?
The octoprint server no longer launches. It was running fine for a long time, and now even when I restart the service or the raspberry pi, it doesn't launch. I get a screen instead telling me the server isn't running. This started after I installed PSU Control, PolarCloud, and Print Anywhere, and after I did a pip upgrade and sudo apt-get upgrade. So any of them could have caused it.

What did you already try to solve it?
Tried to restart the service and the raspberry pi. Multiple times. Read existing support about it. Looked at octoprint.log

Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, octoprint.log, serial.log or output on terminal tab, ...)
octoprint, version 1.3.10
Prusa i3 mk3s
Latest firmware
octoprint.log:

2019-03-31 05:55:50,320 - octoprint.plugins.discovery - INFO - Registered OctoPrint instance "PrusaPrint πŸ˜‰" for SSDP
2019-03-31 05:55:50,600 - octoprint.server - INFO - Listening on http://127.0.0.1:5000
2019-03-31 05:55:50,941 - octoprint.plugins.pluginmanager - INFO - Loaded notice data from disk, was still valid
2019-03-31 05:55:51,189 - octoprint.plugins.bedlevelvisualizer - INFO - OctoPrint-BedLevelVisualizer loaded!
2019-03-31 05:55:51,284 - octoprint.plugins.ipOnConnect - INFO - ipOnConnectPlugin: 192.168.1.135
2019-03-31 05:55:51,500 - octoprint.plugins.pluginmanager - INFO - Loaded plugin repository data from disk, was still valid
2019-03-31 05:56:01,210 - octoprint.plugins.pluginmanager - INFO - Loaded notice data from disk, was still valid

Looks like Octoprint is online as expected, try sshing to the Pi and running this to make sure:

curl http://localhost:5000/

Assuming that works, I'd check haproxy. If you do ps waxu | grep haproxy you should see three /usr/sbin/haproxy services. You can also check to see if the service started properly:

sudo service haproxy status

If it isn't, look in /var/log/syslog and /var/log/haproxy.log.

pi@octopi:~ $ curl http://localhost:5000/
curl: (7) Failed to connect to localhost port 5000: Connection refused