For the working one, I can enter commands through cutecom, and ifconfig ecm0 responds correctly
Otherwise, with the other I cannot enter any command
just this line loop:
swi-mdm9x28-wp user.err kernel: [ 49.040354] wait_for_irsc_completion: waiting for IPC Security Conf.
Like the boot steps are not finished and give me no access to the board
Suggest you downgrade to fw R9, and then use “swiflash -m wp77xx -r” to erase user app partition.
Please see here
I can’t download the R9 version:
https://source.sierrawireless.com/resources/airprime/software/wp77xx/wp77xx-firmware-release-9/#sthash.Z2l3OrCm.dpbs
Seems the whole source website has problem.
I cannot even download r12.
…
I also found these logs on the broken one:
Jan 6 00:49:23 swi-mdm9x28-wp user.err kernel: [ 83.821012] usb 1-1: device not accepting address 5, error -110
Jan 6 00:49:23 swi-mdm9x28-wp user.err kernel: [ 83.826015] usb usb1-port1: unable to enumerate USB device
Jan 6 00:49:23 swi-mdm9x28-wp user.info kernel: [ 83.832360] msm_hsic_host 7c00000.hsic_host: HSIC-USB in low power mode
No idea what it means, probably first try to erase user partiton
I found the R11, downgrade my board, and I managed to use the swiflash -r command which erased the board
After that I can connect by ssh 
Mangoh should correct swiflash -r option for the new release
Thank you for your time @jyijyi !!!