Feature has a pattern in relation to class but does not enhance classifier to predict class

Question

I have a feature x that when I plot it again my class variable y it shows some sort of pattern, i.e. it is obvious that x has a relation with y, but when I add the x to my logistic model it reduce the model accuracy. I want to know the reason, I thought that maybe there is a different distribution in my training and testing data, that lead to this, and checked this hypothesis, the result was that distributions are different. In general case any idea is appreciated.