As a prepper I have studied Normalcy Bias, it is a 'glitch' in our brain function that often disallows the brain to accept the fact that something is occurring even while the brain is receiving incontrovertible data that that very thing is happening......
The problem is it works both ways. One can get so caught up in what they believe (adding in the complexity of confirmation bias) that they just view what confirms their belief and if anyone disagrees, they think they are the ones suffering normalcy bias, when in fact, because they are in a confirmation bias loop, they are actually experiencing a 'normalcy bias' to their own belief.
Just an 'out there' example, let's take someone who is hyper obsessed with reptilian alien conspiracies. All they do is read about reptilian alien conspiracies and sites that promote it. They are in a confirmation bias loop so to them, seeing the reptilian alien conspiracy is 'normal' (even if it is an abnormal belief). They will accuse someone who doesn't see it of having 'normalcy bias' due to the 'glitch', but in reality, they are surrounding themselves with so much confirmation of their belief, theirs is the mind that refuses to accept outside data.
Y2K is a good example of this. I remember 'normalcy bias' being thrown out a lot by preppers then, against those who didn't think anything would happen because they feed themselves with so much data confirming it that the disaster was the normal accepted event in their own minds.
Normalcy bias doesn't impact just those who occupy 'common knowledge' thinking. It impacts everyone as we all have beliefs that we reinforce and confirm despite outside evidence (because we put ourselves in a confirmation bias loop).