@argo I can confirm (same as @carcamerarig), the issue persists with M569 ... V0.
This time there was one interesting variation, instead of a "thump" one of the two motors decided to stop working altogether, so I was suddenly printing diagonally. Then the console in DWC was flooded with "short to ground" errors:
Interestingly this was a different motor than the one that is always skipping (in my build drivers 5 and 6 are the A and B of CoreXY). Perhaps I could move A and B to another set of drivers.
I grabbed an M122 dump when this happened in case it's useful:
=== Diagnostics ===
RepRapFirmware for Duet 3 Mini 5+ version 3.3beta2 running on Duet 3 Mini5plus Ethernet (standalone mode)
Board ID: NY57W-W096U-D65J0-40KMU-NP03Z-ZKK2Z
Used output buffers: 3 of 40 (14 max)
=== RTOS ===
Static ram: 99720
Dynamic ram: 108484 of which 176 recycled
Never used RAM 32468, free system stack 119 words
Tasks: NETWORK(ready,207) ETHERNET(notifyWait,550) HEAT(delaying,293) CanReceiv(notifyWait,943) CanSender(notifyWait,358) CanClock(delaying,340) TMC(notifyWait,100) MAIN(running,314) IDLE(ready,20) AIN(delaying,260)
Owned mutexes:
=== Platform ===
Last reset 01:37:52 ago, cause: software
Last software reset at 2021-04-07 16:20, reason: User, GCodes spinning, available RAM 35540, slot 0
Software reset code 0x0003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x00000000 BFAR 0xe000ed38 SP 0x00000000 Task MAIN Freestk 0 n/a
Error status: 0x00
Aux0 errors 0,0,0
Aux1 errors 0,0,0
Supply voltage: min 0.0, current 23.9, max 24.2, under voltage events: 0, over voltage events: 0, power good: yes
Heap OK, handles allocated/used 99/2, heap memory allocated/used/recyclable 2048/82/0, gc cycles 0
Driver 0: position 99200, standstill, SG min/max 0/72, read errors 0, write errors 1, ifcnt 40, reads 15989, writes 18, timeouts 274, DMA errors 0, failedOp 0x41
Driver 1: position 0, standstill, SG min/max 0/100, read errors 0, write errors 1, ifcnt 41, reads 16253, writes 19, timeouts 9, DMA errors 0, failedOp 0x71
Driver 2: position 5114, standstill, SG min/max 0/50, read errors 0, write errors 1, ifcnt 41, reads 15966, writes 19, timeouts 296, DMA errors 0, failedOp 0x71
Driver 3: position 0, standstill, SG min/max 0/60, read errors 0, write errors 1, ifcnt 41, reads 16198, writes 19, timeouts 64, DMA errors 0, failedOp 0x6f
Driver 4: position 0, standstill, SG min/max 0/48, read errors 0, write errors 1, ifcnt 35, reads 16267, writes 13, timeouts 1, DMA errors 0, failedOp 0x06
Driver 5: position 0, standstill, SG min/max 0/510, read errors 0, write errors 1, ifcnt 43, reads 16203, writes 19, timeouts 59, DMA errors 0, failedOp 0x6a
Driver 6: position 0, short-to-ground, standstill, SG min/max 0/510, read errors 0, write errors 1, ifcnt 42, reads 16258, writes 19, timeouts 4, DMA errors 0, failedOp 0x01
Date/time: 2021-04-07 17:58:10
Cache data hit count 4294967295
Slowest loop: 125.41ms; fastest: 0.08ms
=== Storage ===
Free file entries: 9
SD card 0 detected, interface speed: 22.5MBytes/sec
SD card longest read time 100.7ms, write time 30.0ms, max retries 0
=== Move ===
DMs created 83, maxWait 4423638ms, bed compensation in use: mesh, comp offset 0.000
=== MainDDARing ===
Scheduled moves 25385, completed moves 25385, hiccups 0, stepErrors 0, LaErrors 0, Underruns [3, 1369, 0], CDDA state -1
=== AuxDDARing ===
Scheduled moves 0, completed moves 0, hiccups 0, stepErrors 0, LaErrors 0, Underruns [0, 0, 0], CDDA state -1
=== Heat ===
Bed heaters = 0 -1, chamberHeaters = -1 -1
Heater 0 is on, I-accum = 0.3
Heater 1 is on, I-accum = 0.4
=== GCodes ===
Segments left: 0
Movement lock held by null
HTTP is idle in state(s) 0
Telnet is idle in state(s) 0
File is doing "G1 X136.015 Y157.355 E0.04029" 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
Code queue is empty.
=== CAN ===
Messages queued 52892, send timeouts 52889, received 0, lost 0, longest wait 0ms for reply type 0, peak Tx sync delay 0, free buffers 17 (min 17)
Last cancelled message type 30 dest 127
=== Network ===
Slowest loop: 179.42ms; fastest: 0.03ms
Responder states: HTTP(0) HTTP(0) HTTP(0) HTTP(0) FTP(0) Telnet(0), 0 sessions
HTTP sessions: 1 of 8
- Ethernet -
State: active
Error counts: 0 0 0 0 0
Socket states: 5 2 2 2 2 2 0 0
When I restarted the Mini5+ (via Emergency Stop in DWC) the errors stopped and I restarted the print again, this time the usual skipping happened during the very first travel move of the print so I did not have to wait long.
I have yet to find a particular mode that works. My board is being exchanged via warranty due to an unrelated issue (SD card problems) so I guess we'll see if switching to another board helps; I doubt it will but it's one more data point. 
Cheers,
Ben.
