It seems your board is healthier than mine, my board is showing failure almost every round. Although your board is failing at ‘testing 54’ and mine is ‘testing 48’, it’s the 7th byte from LSB. (in contrast, the problematic byte in the old post is the 3rd byte). You can modify the loop range in test_bitspread_comparison()
to the problematic byte, for example 48 to 56, in order to accelerate your test.
I’m also interested in underclocking DRAM, but I don’t know how to do that. Is there any tutorial for that?