I love Octoprint, it definitely makes the printer use soo much nicer than SD card swapping and perpetual firmware updates for tweaking!!
But.. after the 40th hour of a 60('ish) hour print.. I got this! 
If anyone has an idea why?
"Unexpected error while reading serial port, please consult octoprint.log for details: SerialException: 'device reports readiness to read but returned no data (device disconnected or multiple access on port?)' @ comm.py:_readline:2417
Please see https://faq.octoprint.org/serialerror for possible reasons of this.
Changing monitoring state from "Printing" to "Offline (Error: SerialException: 'device reports readiness to read but returned no data (device disconnected or multiple access on port?)' @ comm.py:_readline:2417)"
Connection closed, closing down monitor"
The Printer was working unattended for a very long time, nothing moving anywhere near it to shake connections loose, nothing on the network to mess with the octoprint server etc.. just lost connection?
Is this a common problem via USB connection to printer control boards from SBC's? Is there a way to attach a hat or other communication bus system? I certainly hope Printers get away from the archaic USB 1.0 square plug.. hard to find good cables for them, at least 2.0 cables are a dime a dozen to pickupm and readily available.
Raspberry Pi 3, Octoprint 1.3.7, Tevo Tornado with stock Marlin firmware (not sure what version on this Gen V1.4 board). I do have a .log file but don't see a place to attach it here.
Any idea's to fix this, or should I print large items from SD cards only for now?
Now to the tedious Gcode editing to resume print.