- a family that are members of Bible believing churches with credible pastors for decades being accused of being Muslim sleepers
- a conservative Christian who suddenly spouts Pashto
Being a member of a good Church, although a good thing, really does not allow us to see into one's heart... When trials come, they may abandon the Faith that they once claimed. The Apostle John talked about this in his first epistle
1 John 2:19 They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us.
I.e., these kind of things were happening in the First Century. Maybe they weren't spouting praises to Allah, but at the time of trials they were praising whatever deity Satan was pushing.
The fire of the furnace separates the dross from the precious.
No, I am not the judge - but I would not say that the examples you cited don't make sense. Similar actions have been all too common in the past.
The only credible explanation for Bob Bergdahl's behavior is that he has apostatized from the Christian faith. He didn't spend years growing a Muslin style beard or learning Arabic and verses from the Koran as a hobby.
True, it could have been an elaborate, multi-decade fake job. Not likely, but possible. Towards what end?