Ok - so it happend while I was using the filament-error to calibrate the E-Steps and non-linear extrusion. I set the error margin almost to zero +-0.5% and so there are a lot of events generated.
The following macro can trigger the bug
Content of 0:/macros/test-event-system.g
Contnet of 0:/sys/filament-error.g
if exists(global.ignoreMFMevents) && global.ignoreMFMevents == true M99Have at least one DWC session open.
Call the macro 0:/macros/test-event-system.g
Result in journalctl
Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Starting macro file filament-error.g on channel Autopause Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [warn] M957: a similar event is already queued Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Received file abort request on channel Autopause for the last file Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Aborted macro file filament-error.g Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Starting macro file filament-error.g on channel Autopause Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [warn] M957: a similar event is already queued Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Received file abort request on channel Autopause for the last file Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Aborted macro file filament-error.g Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Starting macro file filament-error.g on channel Autopause Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [warn] Resending packet #1 (request GetObjectModel) Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [fatal] Abnormal program termination Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [fatal] Update task faulted Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: System.Text.Json.JsonReaderException: The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true. LineNumber: 0 | BytePositionInLine: 0. Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: at System.Text.Json.ThrowHelper.ThrowJsonReaderException(Utf8JsonReader& json, ExceptionResource resource, Byte nextByte, ReadOnlySpan`1 bytes) Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: at System.Text.Json.Utf8JsonReader.Read() Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: at DuetControlServer.Model.Updater.UpdateModel(Int32 offset, Boolean last) in /home/runner/work/DuetSoftwareFramework/DuetSoftwareFramework/src/DuetControlServer/Model/Updater.cs:line 150 Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: at DuetControlServer.Model.Updater.Run() in /home/runner/work/DuetSoftwareFramework/DuetSoftwareFramework/src/DuetControlServer/Model/Updater.cs:line 296 Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [warn] Resending packet #0 (request GetObjectModel) Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [warn] M957: a similar event is already queued Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [warn] Failed to find query for object model response Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Received file abort request on channel Autopause for the last file Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Aborted macro file filament-error.g Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [warn] HTTP: Aborting orphaned macro file 0:/macros/test-event-system.g Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Aborted macro file 0:/macros/test-event-system.g Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [warn] HTTP: ==> Cancelling unfinished starting code: M98 P"0:/macros/test-event-system.g" Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [warn] Daemon: Aborting orphaned macro file daemon.g Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Aborted macro file daemon.g Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Event logging stopped Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [fatal] Update task faulted Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: System.Text.Json.JsonReaderException: The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true. LineNumber: 0 | BytePositionInLine: 0. Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: at System.Text.Json.ThrowHelper.ThrowJsonReaderException(Utf8JsonReader& json, ExceptionResource resource, Byte nextByte, ReadOnlySpan`1 bytes) Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: at System.Text.Json.Utf8JsonReader.Read() Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: at DuetControlServer.Model.Updater.UpdateModel(Int32 offset, Boolean last) in /home/runner/work/DuetSoftwareFramework/DuetSoftwareFramework/src/DuetControlServer/Model/Updater.cs:line 150 Feb 20 09:33:57 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: at DuetControlServer.Model.Updater.Run() in /home/runner/work/DuetSoftwareFramework/DuetSoftwareFramework/src/DuetControlServer/Model/Updater.cs:line 296 Feb 20 09:33:58 Meltingplot-MBL-480-vaswsq DuetControlServer[405]: [info] Application has shut down Feb 20 09:33:58 Meltingplot-MBL-480-vaswsq systemd[1]: duetcontrolserver.service: Main process exited, code=exited, status=70/SOFTWARE -- Subject: Unit process exitedEDIT: at the second attempt I was not able to reproduce it! Maybe it is related to [warn] Resending packet #1 (request GetObjectModel) as in the first try I saw many of these warnings and after a reboot, these warmings are gone and I can't reproduce the update thread bug.