The phrase "incomprehensible reason" is correct and usable in written and spoken English.
You can use it when you are trying to describe something that is impossible to understand. For example: "I could not find any understandable justification for his actions, so I concluded that there must have been an incomprehensible reason for his behavior."
And yet for some incomprehensible reason, these are what everyone chooses.
It's bad enough that Donald Trump has to look serious around the victims of a school massacre, which he finds impossible, for some incomprehensible reason.
The main difference between the parties in this regard is that Republican candidates feel obliged for some incomprehensible reason to make obeisance to Donald J. Trump, and perhaps go off to eat mediocre pizza with him.
For some unexplained (and incomprehensible) reason, however, Taranto seems to think that when both parties involved in a sexual assault are drunk, more often than not the male party is wrongfully blamed.
When Night Time, My Time finally appeared in 2013, it was such an accomplished pop record that it appeared on a number of best-of-the-year lists in the UK despite the fact that – for some incomprehensible reason – it's not officially out in Britain until March.
For some incomprehensible reason that still remains a complete mystery, this year's elections are no longer governed by the usual determinants of polling.
Even when we say 'yes we agree', they stab us in the side or the back, for absolutely incomprehensible reasons," he said.
She awakens to a call from Don, who seems alarmed for incomprehensible reasons.
Now she turns up regularly to give bizarre interviews, express her often controversial opinions and get divorced for incomprehensible reasons after 16 days of marriage.
Over the next half-century Italian governments came and went at dizzying speed and for near-incomprehensible reasons.
When she wanders off, for "incomprehensible, unknowable" reasons, he becomes a Romantic hero possessed: "I can recount just about every step of my search for her and many of the key incidents of our relationship before then.
