I can also confirm this is a problem for me as well. I am using a 6HC with SBC. I have to power cycle the whole machine to get it through the issue. Simply rebooting the Pi4 will not solve the problem.
Here is an M122 after reboot.
m122
=== Diagnostics ===
RepRapFirmware for Duet 3 MB6HC version 3.5beta2 (2023-02-08 15:27:50) running on Duet 3 MB6HC v1.0 or earlier (SBC mode)
Board ID: 08DJM-956L2-G43S4-6J1FD-3SJ6T-TB6QH
Used output buffers: 1 of 40 (17 max)
=== RTOS ===
Static ram: 154344
Dynamic ram: 85824 of which 2892 recycled
Never used RAM 99556, free system stack 200 words
Tasks: SBC(ready,0.7%,418) HEAT(notifyWait,0.0%,325) Move(notifyWait,0.0%,342) CanReceiv(notifyWait,0.0%,798) CanSender(notifyWait,0.0%,335) CanClock(delaying,0.0%,340) TMC(notifyWait,6.0%,90) MAIN(running,92.5%,160) IDLE(ready,0.8%,30), total 100.0%
Owned mutexes: HTTP(MAIN)
=== Platform ===
Last reset 00:01:45 ago, cause: power up
Last software reset at 2023-03-10 21:36, reason: User, Gcodes spinning, available RAM 99556, slot 1
Software reset code 0x6003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x00400000 BFAR 0x00000000 SP 0x00000000 Task SBC Freestk 0 n/a
Error status: 0x00
Step timer max interval 132
MCU temperature: min 23.5, current 24.4, max 37.5
Supply voltage: min 0.2, current 24.0, max 24.1, under voltage events: 0, over voltage events: 0, power good: yes
12V rail voltage: min 0.2, current 12.2, max 12.2, under voltage events: 0
Heap OK, handles allocated/used 99/15, heap memory allocated/used/recyclable 2048/1472/1232, gc cycles 0
Events: 0 queued, 0 completed
Driver 0: standstill, SG min 0, mspos 8, reads 52289, writes 11 timeouts 0
Driver 1: standstill, SG min 0, mspos 8, reads 52289, writes 11 timeouts 0
Driver 2: standstill, SG min 0, mspos 8, reads 52282, writes 18 timeouts 0
Driver 3: standstill, SG min 0, mspos 8, reads 52282, writes 18 timeouts 0
Driver 4: standstill, SG min 0, mspos 8, reads 52282, writes 18 timeouts 0
Driver 5: standstill, SG min 0, mspos 8, reads 52283, writes 18 timeouts 0
Date/time: 2023-03-11 11:47:31
Slowest loop: 2.36ms; fastest: 0.06ms
=== Storage ===
Free file entries: 20
SD card 0 not detected, interface speed: 37.5MBytes/sec
SD card longest read time 0.0ms, write time 0.0ms, max retries 0
=== Move ===
DMs created 125, segments created 0, maxWait 0ms, bed compensation in use: none, comp offset 0.000
no step interrupt scheduled
=== DDARing 0 ===
Scheduled moves 0, completed 0, hiccups 0, stepErrors 0, LaErrors 0, Underruns [0, 0, 0], CDDA state -1
=== DDARing 1 ===
Scheduled moves 0, completed 0, hiccups 0, stepErrors 0, LaErrors 0, Underruns [0, 0, 0], CDDA state -1
=== Heat ===
Bed heaters 0 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1, chamber heaters -1 -1 -1 -1, ordering errs 0
Heater 1 is on, I-accum = 0.0
=== GCodes ===
Movement locks held by null, null
HTTP* is doing "M122" in state(s) 0
Telnet is idle in state(s) 0
File is idle in state(s) 0
USB is idle in state(s) 0
Aux is idle in state(s) 0
Trigger* is idle in state(s) 0
Queue is idle in state(s) 0
LCD is idle in state(s) 0
SBC is idle in state(s) 0
Daemon* is idle in state(s) 0
Aux2 is idle in state(s) 0
Autopause is idle in state(s) 0
File2 is idle in state(s) 0
Queue2 is idle in state(s) 0
Q0 segments left 0, axes/extruders owned 0x80000003
Code queue 0 is empty
Q1 segments left 0, axes/extruders owned 0x0000000
Code queue 1 is empty
=== Filament sensors ===
Extruder 0: no data received
=== CAN ===
Messages queued 892, received 4517, lost 0, boc 0
Longest wait 3ms for reply type 6053, peak Tx sync delay 49166, free buffers 50 (min 49), ts 528/400/0
Tx timeouts 0,0,127,0,0,0 last cancelled message type 30 dest 127
=== SBC interface ===
Transfer state: 5, failed transfers: 0, checksum errors: 0
RX/TX seq numbers: 3297/3297
SPI underruns 0, overruns 0
State: 5, disconnects: 0, timeouts: 0 total, 0 by SBC, IAP RAM available 0x26934
Buffer RX/TX: 0/0-0, open files: 0
=== Duet Control Server ===
Duet Control Server version 3.5.0-beta.2 (2023-02-08 11:47:09)
Code buffer space: 4096
Configured SPI speed: 8000000Hz, TfrRdy pin glitches: 0
Full transfers per second: 14.41, max time between full transfers: 286.2ms, max pin wait times: 34.3ms/7.2ms
Codes per second: 0.60
Maximum length of RX/TX data transfers: 4505/804