Jehovah's Witnesses were gassed at Auschwitz., The Guardian. it might have happened, but not because they were devotees, rather such individuals, were caught up as members of another group. I can think of one lady from my youth, who could have been a witness, married to a jew, and who refused to divorce him according to the demands of the Nazi race laws, both had to wear the yellow Star of David in the 1930s and were gone by 1945. gone.
About this story of 90, mostly --46 boys, 44 girls baptized, family, or an "organized" wave could have be factor, we will not have heard the last of it. The sources have never lied to me.