Connected for a while, now cannot connect to printer

What is the problem?
I built a new Octoprinter today and could browse using various browsers on different computers. Now it cannot connect.
What did you already try to solve it?
Restarted browsers, logged in again. Tried different port speeds.
Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, octoprint.log, serial.log or output on terminal tab, ...)
Latest version, just updated today using Octopi's browser screen.
I can connect to the Octopi via a browser, but the Raspberry Pi 3b+ cannot connect to the printer even tho it did so 30 minutes ago. I cannot test rebooting the rPi or Octoprint as it warns this could stop the current printjob.

Connecting to: /dev/ttyUSB0
Changing monitoring state from "Detecting serial port" to "Error: Connection error, see Terminal tab"
Unexpected error while connecting to serial port: AUTO IOError: '[Errno 5] Input/output error' @ comm.py:_openSerial:2478 (hook default)

Connecting to: /dev/ttyUSB0
Changing monitoring state from "Offline" to "Error: Connection error, see Terminal tab"
Unexpected error while connecting to serial port: /dev/ttyUSB0 IOError: '[Errno 5] Input/output error' @ comm.py:_openSerial:2478 (hook default)

What printer? What type of update did you perform?

Ender 3.

Upgrade is when you log onto the Octoprint webpage and it says "Upgrade available! Click here to upgrade Octoprint!"
I've rebooted and it seems it may be ok for now.