This issue is not about the software as far as I see it. I am pretty sure that the software module was implemented and tested successfully against the module requirements. It is a systems engineering process issue, that is a concern.
During design, implementation and certification the analysis never revealed that an important component is guaranteed to fail every 248 days. This is evident because had it been analysed then there would already be an aircrew/maintenance action in place. The aim of the certification and analysis process is to drive out and mitigate all potential latent defects to an acceptable probability/consequence level. In this case the process failed spectacularly. Luckily the outcome was unspectacular and easy to manage, but the failure of the process is still of great concern.