From what I've heard (FWIW), Airbus released a version of the software for one of the flight computers that removed SEU protections (hence grounding affected models until they could be downgraded to the previous version).

There was still hardware redundancy though. Operation of the plane's elevator switched to a secondary computer. Presumably it was also running the same vulnerable software, but they diverted and landed early in part to minimize this risk.

So not just redundancy but layers of redundancy.