EBC-RS08-24B1C SD boot / bootloader help

Hi, does anyone have experience with the Advantech EBC-RS08, Part No. EBC-RS08-24B1C, especially the version used as an Enpal gateway? I am trying to boot Linux from the SD card without modifying the internal eMMC. The hardware appears to be based on the NXP i.MX8M Mini and seems very similar to the RSB-3730 A2.

I have already tested several official RSB-3730 images/bootloaders including A1031, A1045 and D0060, used SW1 in the documented SD boot position, and found that jumper J2 changes the boot behavior.

A1031 gives:
power_bd71837_init
Trying to boot from MMC1
MMC: no card present

D0060 gives:
Can't find PMIC:PCA9450
DDRINFO: DRAM rate 3000MTS
Training FAILED

I also verified that the bootloader is correctly written to the SD card at the expected offset.

Does anyone know the actual hardware/board revision used in EBC-RS08-24B1C, the function of J2, the correct SD boot procedure, or which RSB-3730 bootloader/image is compatible with this specific unit? Any documentation or experience with this OEM board would be very helpful.

EBC-RS08-24B1C is a customized product from Advantech. If you have any questions regarding this product, please contact our PSM or sales department. We have dedicated one-on-one technical support.

Regarding the startup of RSB-3730, you can refer to the following link.

RSB-3730 Yocto42 User Guide | AIM-Linux Developer Center

Thank you!