AM6442: Booting from eMMC 5.1 HS400 fails

Tool/software:

Dear TI Support,

we have a custom board without SD Card but with eMMC.

Our first prototype is using eMMC Micron MTFC16GAPALBH-AAT which is a 16GB density. For second proto we want to use Micron MTFC64GBCAQTC-AAT which is a 64GB density. Booting the first prototype from eMMC is working fine; but when I apply the same steps on the 64GB device, the board will not boot from eMMC bootmode.

I'm using the following sequence :  

1/ boot via UART bootmode and upload the R5/A53 SPL and Uboot,
2/ in Uboot I transfer the same files via TFTP and write them via Uboot commands to the BOOT0 partition of the eMMC,
3/ next I reboot the board in eMMC bootmode : booting works with the 16GB but not with the 64GB  (with exact same binaries and programming sequence).

The information about the 16GB device is : 

=> mmc info
Device: mmc@fa10000
Manufacturer ID: 13
OEM: 4e
Name: S0J56X
Bus Speed: 200000000
Mode: HS200 (200MHz)
Rd Block Len: 512
MMC version 5.1
High Capacity: Yes
Capacity: 14.8 GiB
Bus Width: 8-bit
Erase Group Size: 512 KiB
HC WP Group Size: 8 MiB
User Capacity: 14.8 GiB WRREL
Boot Capacity: 31.5 MiB ENH
RPMB Capacity: 4 MiB ENH
Boot area 0 is not write protected
Boot area 1 is not write protected

while the 64 GB device : 

=> mmc info
Device: mmc@fa10000
Manufacturer ID: 13
OEM: 4e
Name: AAM20F
Bus Speed: 200000000
Mode: HS200 (200MHz)
Rd Block Len: 512
MMC version 5.1
High Capacity: Yes
Capacity: 59.3 GiB
Bus Width: 8-bit
Erase Group Size: 512 KiB
HC WP Group Size: 16 MiB
User Capacity: 59.3 GiB WRREL
Boot Capacity: 31.5 MiB ENH
RPMB Capacity: 4 MiB ENH
Boot area 0 is not write protected
Boot area 1 is not write protected

I'm following this sequence for writing for both devices : 

mmc dev 0;
mmc rescan;
mmc dev 0 1;
tftp ${loadaddr} tiboot3.bin;
mmc write ${loadaddr} 0x0 0x800;
tftp ${loadaddr} tispl.bin;
mmc write ${loadaddr} 0x800 0x1000;
tftp ${loadaddr} u-boot.img;
mmc write ${loadaddr} 0x1800 0x2000;
mmc partconf 0 1 1 1;
mmc bootbus 0 2 0 0;

I have tried to specify a different speed setting for the 64GB since it didn't work with the original setting above, but this didn't solve the issue (speed mode 11 (HS400) was not supported although it was enabled in the .config, but speed mode 10 (HS200) seems to be accepted) :

mmc dev 0;
mmc rescan 10;
mmc dev 0 1 10;
tftp ${loadaddr} tiboot3.bin;
mmc write ${loadaddr} 0x0 0x800;
tftp ${loadaddr} tispl.bin;
mmc write ${loadaddr} 0x800 0x1000;
tftp ${loadaddr} u-boot.img;
mmc write ${loadaddr} 0x1800 0x2000;
mmc partconf 0 1 1 1;
mmc bootbus 0 2 0 1;

From the MMC information above, I can see that another parameter is different : HC WP Group Size  8 MiB versus 16 MiB.

can this be the reason for not being able to boot the 64GB device in eMMC bootmode?

How can I get around this?

kind regards,