The primary was being inspected and the secondary failed.
There were two independent systems.
Which is why many systems on most airliners are redundant in threes (though under double fault may operate in a degraded mode).
There was a third system, the fallback they used to prevent loss of life, legacy systems and a system shutdown.
You can argue thats not a sufficient third redundancy, I don't have enough context to throw an opinion out there on the safety of this particular infrastructure project.
I am confident that the fallback process was considered and kept in place as the tertiary backup.
Excellent point though. It took me some thinking to put myself back in SRM mindset and what they'd have considered here.
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> The primary was being inspected
So in reality you didn't have two systems.
otherwise you would have shut down operations until you had another connection live, so you had 2 online connections.