Hi All,
I'm quite new to Octoprint. I have two FreeBSD iocages each running an Octoprint installation. The first jail wich is connected to my Creaity CR-10S Pro V2 is working properly. The second one connects to a MP Select Mini V2...better said SHOULD connect 
I'm already using the connection fix for Malyan/Monoprice but it will not connect at all. I already enabled serial debugging but unfortunately cannot find an usable information.
Would be very appreciated if someone has an idea how to fix the issue. Details are listed below.
Thank you in advance, greetings from Berlin and stay save!
Martin
Host OS: FreeNAS-11.3-U2
Jail OS: FreeBSD 11.3-RELEASE-p7
Octoprint version: 1.4.0 with OctoPrint Malyan Connection Fix Plugin (https://github.com/OctoPrint/OctoPrint-MalyanConnectionFix)
Printer: Monoprice Select Mini V2
Printer firmware: latest V41 (it is currently printing so i cannot check the exact version number )
Terminal output:
Connecting to: /dev/cuaU0
Using Malyan/Monoprice Connection Fix Plugin to create serial connection
Changing monitoring state from "Offline" to "Opening serial port"
Connected to: Serial<id=0x8115a0790, open=True>(port='/dev/cuaU0', baudrate=115200, bytesize=8, parity='N', stopbits=1, timeout=10.0, xonxoff=False, rtscts=False, dsrdtr=
Starting baud rate detection...
Changing monitoring state from "Opening serial port" to "Detecting baudrate"
Trying baudrate: 115200
Send: N0 M110 N0*125
Baudrate test retry #1
Send: N0 M110 N0*125
Unexpected error while reading serial port, please consult octoprint.log for details: SerialException: 'device reports readiness to read but returned no data (device disc
Please see https://faq.octoprint.org/serialerror for possible reasons of this.
Changing monitoring state from "Detecting baudrate" to "Offline (Error: SerialException: 'device reports readiness to read but returned no data (device disconnected or mu
Connection closed, closing down monitor
Serial debug log:
2020-04-23 12:31:31,641 - Enabling serial logging
2020-04-23 12:31:44,880 - Connecting to: /dev/cuaU0
2020-04-23 12:31:44,880 - Using Malyan/Monoprice Connection Fix Plugin to create serial connection
2020-04-23 12:31:44,883 - Changing monitoring state from "Offline" to "Opening serial port"
2020-04-23 12:31:44,886 - Connected to: Serial<id=0x8115bbb10, open=True>(port='/dev/cuaU0', baudrate=115200, bytesize=8, parity='N', stopbits=1, timeout=10.0, xonxoff=False, rtscts=False, dsrdtr=False), starting monitor
2020-04-23 12:31:44,886 - Starting baud rate detection...
2020-04-23 12:31:44,887 - Changing monitoring state from "Opening serial port" to "Detecting baudrate"
2020-04-23 12:31:45,891 - Trying baudrate: 115200
2020-04-23 12:31:45,893 - Send: N0 M110 N0*125
2020-04-23 12:31:55,959 - Baudrate test retry #1
2020-04-23 12:31:55,962 - Send: N0 M110 N0*125
2020-04-23 12:31:56,746 - 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:2823
2020-04-23 12:31:56,746 - Please see https://faq.octoprint.org/serialerror for possible reasons of this.
2020-04-23 12:31:56,747 - Changing monitoring state from "Detecting baudrate" to "Offline (Error: SerialException: 'device reports readiness to read but returned no data (device disconnected or multiple access on port?)' @ comm.py:_readline:2823)"
2020-04-23 12:31:56,750 - Connection closed, closing down monitor
2020-04-23 12:32:13,368 - Connecting to: /dev/cuaU0
2020-04-23 12:32:13,371 - Using Malyan/Monoprice Connection Fix Plugin to create serial connection
2020-04-23 12:32:13,373 - Changing monitoring state from "Offline" to "Opening serial port"
2020-04-23 12:32:13,374 - Connected to: Serial<id=0x8104c0590, open=True>(port='/dev/cuaU0', baudrate=115200, bytesize=8, parity='N', stopbits=1, timeout=10.0, xonxoff=False, rtscts=False, dsrdtr=False), starting monitor
2020-04-23 12:32:13,376 - Changing monitoring state from "Opening serial port" to "Connecting"
2020-04-23 12:32:13,382 - Send: N0 M110 N0*125
2020-04-23 12:32:25,099 - 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:2823
2020-04-23 12:32:25,101 - Please see https://faq.octoprint.org/serialerror for possible reasons of this.
2020-04-23 12:32:25,102 - Changing monitoring state from "Connecting" to "Offline (Error: SerialException: 'device reports readiness to read but returned no data (device disconnected or multiple access on port?)' @ comm.py:_readline:2823)"
2020-04-23 12:32:25,105 - Connection closed, closing down monitor
Octoprint log:
2020-04-23 12:32:13,373 - octoprint.util.comm - INFO - Changing monitoring state from "Offline" to "Opening serial port"
2020-04-23 12:32:13,376 - octoprint.util.comm - INFO - Changing monitoring state from "Opening serial port" to "Connecting"
2020-04-23 12:32:13,382 - octoprint.util.comm - INFO - M110 detected, setting current line number to 0
2020-04-23 12:32:25,098 - octoprint.util.comm - ERROR - Unexpected error while reading from serial port
Traceback (most recent call last):
File "/data/Octoprint/venv/lib/python2.7/site-packages/octoprint/util/comm.py", line 2823, in _readline
ret = self._serial.readline()
File "/data/Octoprint/venv/lib/python2.7/site-packages/serial/serialposix.py", line 501, in read
'device reports readiness to read but returned no data '
SerialException: device reports readiness to read but returned no data (device disconnected or multiple access on port?)
2020-04-23 12:32:25,100 - octoprint.util.comm - ERROR - Please see https://faq.octoprint.org/serialerror for possible reasons of this.
2020-04-23 12:32:25,102 - octoprint.util.comm - INFO - Changing monitoring state from "Connecting" to "Offline (Error: SerialException: 'device reports readiness to read but returned no data (device disconnected or multiple access on port?)' @ comm.py:_readline:2823)"