I've been told by my teachers not to use んです and から/ので together, but I encounter them sometimes, both by sight and by ear. When I try to use it myself, it's always marked wrong.
For example, I am quite sure the sentence 10時半のバスに乗るんだから、早く支度しなさい。in this link would be considered incorrect by my teacher, but it's stated to be correct here.
jgram also states that んです should never be used with other words/ constructions that also indicate reason, like から、ので、ものですから.
Which of the following are grammatically sound?
んですから / んだから
んですので / んだので
んものですから / んものだから