SOLVED!!!
Resodering pins helped!
On the one hand I'm happy that it worked. On the other i honestly cannot comprehand how is it possible that there is no quality check of such obvious part of process and especially considering the price of this board...
@jay_s_uk said in New Duet 3 Mini with broken wifi?:
@laplacek yep, looks like there's an issue with either the serial pins or the reset pin.
That i'm not sure of, they use an automated test rig and I'm not sure what is tested and what isn't
Well Im sure there is a process, but judging by what happens it does not cover ESP + Duet integration... It speaks a bit, tho, about QA they have there... 
@jay_s_uk said in New Duet 3 Mini with broken wifi?:
the warranty process is usually a member of the duet team give authorisation, you send it back to your supplier and the supplier sends you a new one. shouldn't take more than a few days
F. it I mean I dont have time and will to go through it... I'll resoder it and see how it works... If it doesnt ill go for Octo 
@jay_s_uk said in New Duet 3 Mini with broken wifi?:
@laplacek said in New Duet 3 Mini with broken wifi?:
Running RatOS (i think its klipper-based but Im 3d printing newbie )
Boo!
Hahah. Well... I hear you. On the other hand i sort of lost my trust in Duet already. I do get when something breaks when you use it - it happens. But if a product is now working from a very beggining it's a different story. It tells A LOT about overall development/manufacturing process. It's hard for me to assume that the process is 'otherwise fine'...
Anyways BIG THANKS for help @jay_s_uk ! 
@jay_s_uk said in New Duet 3 Mini with broken wifi?:
@laplacek can you give this a try and post the output?
M552 S-1 M552 S0 M997 S1
M552 S-1
WiFi module stopped
ok
M552 S0
ok
M997 S1
T0:-273.1 /0.0 B:-273.1 /0.0
Trying to connect at 230400 baud: failed
Trying to connect at 115200 baud: failed
Trying to connect at 74880 baud: failed
Trying to connect at 9600 baud: failed
Error: Installation failed due to comm write error
ok
@jay_s_uk said in New Duet 3 Mini with broken wifi?:
And I believe all the duet boards are tested before shipment.
well, wifi was not working in my from start (i was not able to get through M552 S0). The question is if WiFi connection is actually tested in a test process....
@jay_s_uk said in New Duet 3 Mini with broken wifi?:
@laplacek said in New Duet 3 Mini with broken wifi?:
switch to PI + Octopus setup?
Running klipper or RRF?
Running RatOS (i think its klipper-based but Im 3d printing newbie 
)
Hey guys. Couple of days ago I've bought RatRig V-Core 3, and I'm now trying to set up Duet 3 Mini that came with it. Unfortunately I am not able to neither start wifi module (it locks in 'beeing started' state) nor to do the firmware update of the module (M997 S1 ends up with "Error: Installation failed due to comm write error").
M122
=== Diagnostics ===
RepRapFirmware for Duet 3 Mini 5+ version 3.4.1 (2022-06-01 21:06:56) running on Duet 3 Mini5plus WiFi (standalone mode)
Board ID: 51JT6-S196U-D65J0-40KM0-L413Z-R5FR1
Used output buffers: 1 of 40 (1 max)
=== RTOS ===
Static ram: 103684
Dynamic ram: 109988 of which 12 recycled
Never used RAM 28028, free system stack 150 words
Tasks: NETWORK(ready,7.1%,524) HEAT(notifyWait,0.0%,358) Move(notifyWait,0.0%,363) CanReceiv(notifyWait,0.0%,942) CanSender(notifyWait,0.0%,372) CanClock(delaying,0.0%,339) TMC(notifyWait,0.0%,123) MAIN(running,92.0%,412) IDLE(ready,0.1%,29) AIN(delaying,0.8%,273), total 100.0%
Owned mutexes: USB(MAIN)
=== Platform ===
Last reset 00:05:23 ago, cause: power up
Last software reset details not available
Error status: 0x00
MCU revision 3, ADC conversions started 323193, completed 323193, timed out 0, errs 0
Step timer max interval 730
MCU temperature: min 27.1, current 32.6, max 32.9
Supply voltage: min 0.3, current 0.8, max 0.8, under voltage events: 0, over voltage events: 0, power good: no
Heap OK, handles allocated/used 0/0, heap memory allocated/used/recyclable 0/0/0, gc cycles 0
Events: 0 queued, 0 completed
Driver 0: ok, SG min n/a, read errors 0, write errors 0, ifcnt 0, reads 0, writes 0, timeouts 0, DMA errors 0, CC errors 0
Driver 1: ok, SG min n/a, read errors 0, write errors 0, ifcnt 0, reads 0, writes 0, timeouts 0, DMA errors 0, CC errors 0
Driver 2: ok, SG min n/a, read errors 0, write errors 0, ifcnt 0, reads 0, writes 0, timeouts 0, DMA errors 0, CC errors 0
Driver 3: ok, SG min n/a, read errors 0, write errors 0, ifcnt 0, reads 0, writes 0, timeouts 0, DMA errors 0, CC errors 0
Driver 4: ok, SG min n/a, read errors 0, write errors 0, ifcnt 0, reads 0, writes 0, timeouts 0, DMA errors 0, CC errors 0
Driver 5: ok, SG min n/a, read errors 0, write errors 0, ifcnt 0, reads 0, writes 0, timeouts 0, DMA errors 0, CC errors 0
Driver 6: ok, SG min n/a, read errors 0, write errors 0, ifcnt 0, reads 0, writes 0, timeouts 0, DMA errors 0, CC errors 0
Date/time: 1970-01-01 00:00:00
Cache data hit count 702245795
Slowest loop: 4.31ms; fastest: 0.12ms
=== Storage ===
Free file entries: 10
SD card 0 detected, interface speed: 22.5MBytes/sec
SD card longest read time 3.1ms, write time 0.0ms, max retries 0
=== Move ===
DMs created 83, segments created 0, maxWait 0ms, bed compensation in use: none, comp offset 0.000
=== MainDDARing ===
Scheduled moves 0, completed 0, hiccups 0, stepErrors 0, LaErrors 0, Underruns [0, 0, 0], CDDA state -1
=== AuxDDARing ===
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, chamber heaters -1 -1 -1 -1, ordering errs 0
=== 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 idle in state(s) 0
USB is ready with "M122" 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 2906, received 0, lost 0, boc 0
Longest wait 0ms for reply type 0, peak Tx sync delay 0, free buffers 18 (min 18), ts 1616/0/0
Tx timeouts 0,0,1615,0,0,1289 last cancelled message type 30 dest 127
=== Network ===
Slowest loop: 0.19ms; fastest: 0.00ms
Responder states: HTTP(0) HTTP(0) HTTP(0) HTTP(0) FTP(0) Telnet(0), 0 sessions
HTTP sessions: 0 of 8
- WiFi -
Network state is starting2
WiFi module is disabled
Failed messages: pending 0, notready 0, noresp 0
Socket states: 0 0 0 0 0 0 0 0
ok
M552 S1
Turn off the current WiFi mode before selecting a new one
I even started to wonder if ESP U2 is not just soldered in a bad way since it looks a bit uneven...
I know that I can try to send the board back etc, but to be honest I'm not really interested in all the effort and waiting for package to reach the duet, being investigated there, sent back etc. Any community advices before i switch to PI + Octopus setup? 
Since that seems to be a recuring issue (my online read conclusion), maybe Duet shoud add some quality control to the process of producing 200$ board?