Octoprint 1.11.0 stuck on "Connecting" when connecting to Prusa MK3S

What is the problem?

After upgrade to Octoprint 1.11.0 from 1.10.(?) I can no longer connect to the printer. The serial port opens properly, there is active communication between printer and Octoprint, but the connection never advances to "Connected" state.

What did you already try to solve it?

  • Restart Octoprint
  • Restart the host computer
  • Restart the printer
  • Restart the printer and the host computer
  • Restart Octoprint in Safe Mode

Have you tried running in safe mode?

Yes

Did running in safe mode solve the problem?

No

Systeminfo Bundle

You can download this in OctoPrint's System Information dialog ... no bundle, no support!)

octoprint-systeminfo-20250430121325.zip (105.3 KB)

Additional information about your setup

OctoPrint version, OctoPi version, printer, firmware, browser, operating system, ... as much data as possible

Octoprint version: 1.11.0
Host OS version: Build 2023.07.20.144556 with "camera-streamer", based on OctoPi 1.0.0, running on Raspberry Pi 3 Model B Plus Rev 1.3
Printer firmware version: 3.13.2-7080
MMU firmware version: 3.0.1

Log of serial port communication during connection attempt (closed manually, it can go on and on indefinitely):
---- cut here ----
Recv: echo: Last Updated: Oct 20 2023 17:49:53 | Author: (none, default config)
Recv: echo: Free Memory: 2513 PlannerBufferBytes: 1760
Recv: echo:Stored settings retrieved
Recv: adc_init
Recv: Hotend fan type: NOCTUA
Recv: CrashDetect ENABLED!
Recv: Sending 0xFF
Recv: echo:SD card ok
Recv: // action:dump_available
Recv: echo:MMU2:<S0 A322.
Recv: echo:MMU2:>S1
ad.
Recv: echo:MMU2:<S1 A034.
Recv: echo:MMU2:>S2
10.
Recv: echo:MMU2:<S2 A15a.
Recv: echo:MMU2:>S3
7b.
Recv: echo:MMU2:<S3 A34575.
Recv: echo:MMU2:>Wb 5
33.
Recv: echo:MMU2:<Wb A5c.
Recv: echo:MMU2:>W14 14
94.
Recv: echo:MMU2:<W14 A52.
Recv: echo:MMU2:>f0
21.
Recv: echo:MMU2:<f0 Ac5.
Recv: echo:MMU2:>Q0
ea.
Recv: echo:MMU2:<X0 F087.
Recv: echo:MMU2:>R8
81.
Recv: echo:MMU2:<R8 A08d.
Recv: echo:MMU2:>R1b
9e.
Recv: echo:MMU2:<R1b Affbf.
Recv: echo:MMU2:>R1c
88.
Recv: echo:MMU2:<R1c Aff60.
Recv: echo:MMU2:>R4
7b.
Recv: echo:MMU2:<R4 A2860.
Recv: echo:MMU2:>R1a
f5.
Recv: echo:MMU2:<R1a A041.
Recv: echo:MMU2:>Q0
ea.
Recv: echo:MMU2:<X0 F087.
Recv: echo:MMU2:>R8
81.
Recv: echo:MMU2:<R8 A08d.
Recv: echo:MMU2:>R1b
9e.
Recv: echo:MMU2:<R1b Affbf.
Recv: echo:MMU2:>R1c
88.
Recv: echo:MMU2:<R1c Aff60.
Recv: echo:MMU2:>R4
7b.
Recv: echo:MMU2:<R4 A2860.
Recv: echo:MMU2:>R1a
f5.
Recv: echo:MMU2:<R1a A041.
Recv: echo:MMU2:>Q0
ea.
Recv: echo:MMU2:<X0 F087.
Recv: echo:MMU2:>R8
81.
Recv: echo:MMU2:<R8 A08d.
Recv: echo:MMU2:>R1b
9e.
Recv: echo:MMU2:<R1b Affbf.
Recv: echo:MMU2:>R1c
88.
Recv: echo:MMU2:<R1c A5f6.
Recv: echo:MMU2:>R4
7b.
Recv: echo:MMU2:<R4 A2860.
Recv: echo:MMU2:>R1a
f5.
Recv: echo:MMU2:<R1a A041.
Recv: echo:MMU2:>Q0
ea.
Recv: echo:MMU2:<X0 F087.
Recv: echo:MMU2:>R8
81.
Recv: echo:MMU2:<R8 A08d.
Recv: echo:MMU2:>R1b
9e.
Recv: echo:MMU2:<R1b Affbf.
Recv: echo:MMU2:>R1c
88.
Recv: echo:MMU2:<R1c A5f6.
Recv: echo:MMU2:>R4
7b.
Recv: echo:MMU2:<R4 A2860.
Recv: echo:MMU2:>R1a
f5.
Recv: echo:MMU2:<R1a A0*41.
Connection closed, closing down monitor
Changing monitoring state from "Connecting" to "Offline"

---- cut here ----

Same to me on both of my Prusa printers. Had to revert to 1.10 ...

The log excerpt looks fine to me. These are the frequent MMU information from the printer.
It tells me, that the connection is established.

You can suppress these messages by

I submitted a bug report at github. The devs said that it'd be difficult for them to reproduce the bug, so I think it could be helpful if you could confirm it, with system info from your setup. Just don;t forget to enable serial port logging to capture communication between octoprint and the printer before generating the system info bundle

The issue has hopefully been identified and a bugfix release is incoming ASAP. In the meantime, it might help to enable "wait for start on connect" in the serial settings under firmware & protocol.

I have three printers running Octoprint.

All of a sudden all three will not connect, OctoPi starts just find but the printers never are detected. All three are running the latest release.

I find this kinda suspicious, thoughts?

At this moment, "latest" release is V 1.11.1, you are posting to a thread that refers to 1.11.0. So what what version do you have?

Downgrade manually to 1.10.3 or help testing 1.11.1, which is supposed to fix this issue.
If you don't want to do any of these, you can try enabling "wait for start on connect"