hello dmitriy.antonets,
here’s errors reported during flash NX platform.
$ sudo ./flash.sh jetson-xavier-nx-devkit-emmc mmcblk0p1
...
[ 3.1925 ] Boot Rom communication
[ 3.1955 ] tegrarcm_v2 --chip 0x19 0 --rcm rcm_list_signed.xml
[ 3.1981 ] BR_CID: 0x88021911647076c21400000018008140
[ 3.1988 ] RCM version 0X190001
[ 3.2145 ] Boot Rom communication completed
[ 4.2302 ]
[ 5.2348 ] tegrarcm_v2 --isapplet
[ 5.2379 ] Applet version 01.00.0000
[ 5.2565 ]
[ 5.2566 ] Sending BCTs
[ 5.2594 ] tegrarcm_v2 --download bct_bootrom br_bct_BR.bct --download bct_mb1 mb1_bct_MB1_sigheader.bct.encrypt --download bct_mem mem_rcm_sigheader.bct.encrypt
[ 5.2621 ] Applet version 01.00.0000
[ 5.3051 ] Sending bct_bootrom
[ 5.3056 ] [................................................] 100%
[ 5.3065 ] Sending bct_mb1
[ 5.3110 ] [................................................] 100%
[ 5.3153 ] Sending bct_mem
[ 5.3655 ] [................................................] 100%
[ 5.4227 ]
Error: Return value 8
Command tegrarcm_v2 --download bct_bootrom br_bct_BR.bct --download bct_mb1 mb1_bct_MB1_sigheader.bct.encrypt --download bct_mem mem_rcm_sigheader.bct.encrypt
Failed flashing t186ref.
since you had your own board customization, you might using the flash scripts to flash the board instead of using SDKManager.
you should also using correct board configuration files to flash the board, for example, above messages were using jetson-xavier-nx-devkit-emmc.conf configuration file.
thanks