Can anyone explain what is going on tho?
I used the sticks ; one of them gets faulty at a random moment. I bake it; everything seems fine and runs for the next 3 years (lol). same happening again, i bake it and it runs fine again.
Is it the heat cycles?
I'd test with something worthwhile that isn't memtest86, before coming to the conclusion that things are stable. HCI memtest, TM5, Karhu
Assuming from your running 3200CL14 that it's B-die (technically CJR can also do it but loose 14-17-17). B-die is temp sensitive, so anything that doesn't stress it enough to bring the temps up doesn't deserve to be called a memtest, because you don't get a complete picture as to load stability.
DRAM overvolt is common, but different on every board. Some overvolt as much as 0.06V+.
DDR4 is most certainly not good for 1.55V, or even beyond 1.45V. That's only certain ICs (B-die, Rev.E/B, DJR) and still it's a tossup as to whether it will cause you problems down the line, if you have a bad bin B-die for example you should not be so daring with volts.