nRF Connect -> programmer: Thingy91 appears and disappears from 'Select device' menu every ~1 sec

[sirio]

1. Brand new Thingy91 PCA20035 out of the box.
2. Plugging in the USB and turning it on, the nRF Connect Programmer alternates between 'Select device' and 'No devices available' about every second:
   1. Trying to select the device when it's available makes no difference, it goes back to 'No devices available.
   2. I am guessing the bootloader is in a boot loop?
3. If I turn off device and hold SW4 while turning it on, I get device '09F0EDDB4C954321' available stably in the programmer:
   
   1. I assume is the nRF52 bridge, correct?
4. I am then able to update the nRF52 bridge to the latest firmware:
   1.  thingy91_fw_2021-03-04_8e8c6089/img_fota_dfu_hex/thingy91_nrf52_connectivity_bridge_2021-03-04_8e8c6089.hex
   2. I am selecting 'Enable MCUboot'
   3. I am NOT selecting Auto read memory
   4. I use the 'Write' command to update
   5. Completes successfully in ~19 sec
5. After update, device has the same apparent-boot-loop behavior in 2) above
6. If I turn off the device and hold SW3 while turning on, the behavior is the same.
7. If I repeat without SIM card behavior is the same.

Toolchain info:

$ which nrfjprog
/usr/local/bin/nrfjprog

$ nrfjprog --version
nrfjprog version: 10.12.1 
JLinkARM.dll version: 6.88a

$ /Applications/nRF\ Connect.app/Contents/MacOS/nRF\ Connect --version
3.6.1

$ uname -a
Darwin computer.home 19.6.0 Darwin Kernel Version 19.6.0: Tue Jan 12 22:13:05 PST 2021; root:xnu-6153.141.16~1/RELEASE_X86_64 x86_64 i386 MacBookPro16,1 Darwin

[Øyvind]

Hello, 

This is strange behavior which I have not heard of before. How are you connecting the Thingy:91 to your machine? Do you have a USB hub in between?

You have described the perfect solution for when you are not able to get the nRF91 device in the device list. Booting nRF52 device in MCUboot and updating the connectivity bridge, which is what you get in step 3 and 4. 

Have you tried to use another computer or Windows machine?

Kind regards,
Øyvind

[sirio]

Thank you very much for your help.

I changed cable and bypassed the USB hub and this problem resolved.

[Øyvind]

Happy to hear!

Have a good day!