Yes it is somewhat assumed that only one reason was the cause for it not working. But, I see what you mean.

still the answer is "some reason".. because that's how the idiomatic phrase is. if need to use "reasons" for plural so just use "for reasons".. because plural is reffering to collection..

No, it's actually for some reason, (singular) :) because in that case ,for some reason is the same as saying: for a reason it never worked out. a = 1 thing

Hi Peachey,thanks!

*grammar