Serial Monitor at COM3, uploading at COM6

Development Tools IDE 1.x
1

I am seeing a COM3 port active in Tools->Ports and I can open Serial Monitor at COM3. Unfortunately nothing is printed in Serial Monitor. On examining the upload, however I found upload is taking place in COM6. I have Windows 10 laptop and Arduino Nano 33 IOT. I am having this problem very recently. The board was working perfectly fine earlier. Please help.

Below is the relevant part of upload log.

Sketch uses 28620 bytes (10%) of program storage space. Maximum is 262144 bytes.
Global variables use 4348 bytes (13%) of dynamic memory, leaving 28420 bytes for local variables. Maximum is 32768 bytes.
Forcing reset using 1200bps open/close on port COM3
PORTS {COM3, } / {} => {}
PORTS {} / {COM6, } => {COM6, }
Found upload port: COM6
C:\Users\abcd\Documents\ArduinoData\packages\arduino\tools\bossac\1.7.0-arduino3/bossac.exe -i -d --port=COM6 -U true -i -e -w -v C:\Users\abcd\AppData\Local\Temp\arduino_build_70678/bmp280test.ino.bin -R 
Set binary mode
readWord(addr=0)=0x20007ffc
readWord(addr=0xe000ed00)=0x410cc601
readWord(addr=0x41002018)=0x10010305
version()=v2.0 [Arduino:XYZ] Apr 19 2019 14:38:48
chipId=0x10010005
Connected at 921600 baud
readWord(addr=0)=0x20007ffc
readWord(addr=0xe000ed00)=0x410cc601
readWord(addr=0x41002018)=0x10010305
Atmel SMART device 0x10010005 found
write(addr=0x20004000,size=0x34)
writeWord(addr=0x20004030,value=0x10)
writeWord(addr=0x20004020,value=0x20008000)
Device       : ATSAMD21G18A
readWord(addr=0)=0x20007ffc
readWord(addr=0xe000ed00)=0x410cc601
readWord(addr=0x41002018)=0x10010305
Chip ID      : 10010005
version()=v2.0 [Arduino:XYZ] Apr 19 2019 14:38:48
Version      : v2.0 [Arduino:XYZ] Apr 19 2019 14:38:48
Address      : 8192
Pages        : 3968
Page Size    : 64 bytes
Total Size   : 248KB
Planes       : 1
Lock Regions : 16
Locked       : readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
readWord(addr=0x41004020)=0xffff
none
readWord(addr=0x41004018)=0
Security     : false
Boot Flash   : true
readWord(addr=0x40000834)=0x7000a
BOD          : true
readWord(addr=0x40000834)=0x7000a
BOR          : true
Arduino      : FAST_CHIP_ERASE
Arduino      : FAST_MULTI_PAGE_WRITE
Arduino      : CAN_CHECKSUM_MEMORY_BUFFER
Erase flash
chipErase(addr=0x2000)
done in 0.855 seconds

Write 28628 bytes to flash (448 pages)
write(addr=0x20005000,size=0x1000)
writeBuffer(scr_addr=0x20005000, dst_addr=0x2000, size=0x1000)
[====                          ] 14% (64/448 pages)write(addr=0x20005000,size=0x1000)
writeBuffer(scr_addr=0x20005000, dst_addr=0x3000, size=0x1000)
[========                      ] 28% (128/448 pages)write(addr=0x20005000,size=0x1000)
writeBuffer(scr_addr=0x20005000, dst_addr=0x4000, size=0x1000)
[============                  ] 42% (192/448 pages)write(addr=0x20005000,size=0x1000)
writeBuffer(scr_addr=0x20005000, dst_addr=0x5000, size=0x1000)
[=================             ] 57% (256/448 pages)write(addr=0x20005000,size=0x1000)
writeBuffer(scr_addr=0x20005000, dst_addr=0x6000, size=0x1000)
[=====================         ] 71% (320/448 pages)write(addr=0x20005000,size=0x1000)
writeBuffer(scr_addr=0x20005000, dst_addr=0x7000, size=0x1000)
[=========================     ] 85% (384/448 pages)write(addr=0x20005000,size=0x1000)
writeBuffer(scr_addr=0x20005000, dst_addr=0x8000, size=0x1000)
[==============================] 100% (448/448 pages)
done in 0.226 seconds

Verify 28628 bytes of flash with checksum.
checksumBuffer(start_addr=0x2000, size=0x1000) = eb75
checksumBuffer(start_addr=0x3000, size=0x1000) = c73d
checksumBuffer(start_addr=0x4000, size=0x1000) = 215d
checksumBuffer(start_addr=0x5000, size=0x1000) = 98fa
checksumBuffer(start_addr=0x6000, size=0x1000) = b29c
checksumBuffer(start_addr=0x7000, size=0x1000) = 7257
checksumBuffer(start_addr=0x8000, size=0xfd4) = 36af
Verify successful
done in 0.023 seconds
CPU reset.
readWord(addr=0)=0x20007ffc
readWord(addr=0xe000ed00)=0x410cc601
readWord(addr=0x41002018)=0x10010305
writeWord(addr=0xe000ed0c,value=0x5fa0004)
2

For boards with native USB It is normal that the COM port changes. Does the port fall back to COM3 after the upload?

What does Windows device manager think of your board? Do you see it go from COM3 to COM6 and back to COM3 after the upload?

I think that you have to show your sketch so we can have a look at that.

3

Actually my sensors are not working. My program was lopsided. I will mark your answer as solution and post a new thread instead.

4

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