For me there were several things during a long period of time. But the straw of the camel´s back was one: The Philosophical logic fallacies that are obvious in two major issues.
1./ According to the Soc. Jehova God is loving, merciful, forgiving and kind. And he should never ever let his human child burn in a hell. But if you don’t become a JW soon, he will destroy you and all the rest of humans in a total disaster, the BIG A….soon…soon
2./ God sacrificed his one borne son Jesus Christ, so that everyone who believes in him should have eternal life. And the son of God comes down to earth, he is loving careful, merciful, and teach us how to live and how to behave against one another. And we kill him, betray him, humiliate him, put him on a cross, spit on him, and when he dies god takes him back again, and then suddenly everything is forgotten.
Most religious people are totally perplex, when you start to question on these matters
Bugbear