I had a project where we were reaching for the 'cosmic ray' idea. But it turns out it was a supercap that did not hold enough charge on NAND during power off a

I had a project where we were reaching for the 'cosmic ray' idea. But it turns out it was a supercap that did not hold enough charge on NAND during power off and the way NAND ages. It worked when 'new' but as the device aged and was used it the NAND would slowly take extra time to write a page. Eventually the time was just enough that it would mostly write everything. It would also sometimes randomly flip bits here and there depending on where it was in the write cycle.