Quote:I wonder why did the built in memtest not detect even a single one of these errors in my old device?maybe because it's a bad memtest?
i honestly don't know anything about the internal linux memtester, maybe it misses the bad holes, - test zones don't occupy bad pages accidentally. Are they random? If so, after several times, it should overlap with at least one bad page, given how numerous they are. (I really hope the internal tester isn't so dumb to just read back data from cache 
).But if you got many times bad memtest results it means either broken tester or broken memory. Since the former works fine for others, you've got the answer. I hope your new board is OK.
ANT - my hobby OS for x86 and ARM.