Run memtest and maybe a SMART long test.
SMART went fine, but memtest found one of my memory modules to be faulty.
I've replaced the module and will now see if this has fixed the problem.
I'll be back to this topic in one month to tell it's solved or earlier if the problem appears again
BTW, it is strange that it was happening with generic and not with huge kernel, because both of them need to be decompressed to the memory. Really strange. But anyway I think it was about the memory, because the faulty memory region was around ~20MB at the beginning, and I assume that's the region where the kernel is more less decompressed.
Thanks for now and I hope the one month test will succeed.