Simultaneous electrical spikes in different electrical subsystems?
Maybe.
Probably the cause is in the software, the conditions for FAC "healthy", etc...
I mentioned the RTL because both systems 1 and 2 are physically contained in the same unit, so something failing in that unit might affect both systems and for some reason render FACs invalid. But this is just a guess.
Either a dual non related simultaneous failure occurred, which is unlikely but not impossible, or the system is not as redundant as it should be. Computerized systems dissimilar redundancy is not as easy to achieve as it seems, I deem. Unforeseen problems are not only possible but they occur quite often. This might be the case.