yes, that’s right, 8 Mb flash in SM , so no sense to flash in twice.
but as far as I know, a colleague just re-uploaded the same firmware. like for AP.
as far as I understand, in the board remained uboot from v3.5
U-Boot 9344_PX 1.1.4.e (Aug 21 2017 - 16:36:48)
although in 3.5.6 it is already come with:
U-Boot 9344_PX 1.1.4.e (Feb 20 2019 - 10:30:35)
probably uboot it was not updated, because of the same version.
but when you update 3.5.6 to 3.5.6 again, something happened and now uboot halted.