In my experience with ECC RAM on couple thousand servers over a few years, we had a couple machines throw one ECC correctable error and never have an issue again.
It seemed more common for a system to move from no errors to a consistent rate; some moved to one error per day, some 10/day, some to thousands per second which kills performance because of machine check exception handling.
The one off errors could be cosmic rays or faulty ram or voltage droop or who knows what, the repeatable errors are probably faulty ram, replacing the ram resolved the problem.
It seemed more common for a system to move from no errors to a consistent rate; some moved to one error per day, some 10/day, some to thousands per second which kills performance because of machine check exception handling.
The one off errors could be cosmic rays or faulty ram or voltage droop or who knows what, the repeatable errors are probably faulty ram, replacing the ram resolved the problem.