If you want splinter cults, you can easily draw from real-world religions to find reasons for splinter (is the prophet divine or human - or both ? Where does the holy scripture ends ? is everything spiritual good, and if yes, does it mean that the body is inherently evil ? Is lust a human, if base, emotion, or is it unholy ? Are the high priest/esse/s infallible as being the Voice of the Deity, or are they human and prone to error and misinterpretation ?)
You can also have variations on the actual meaning of a powerful symbol. For instance, death is often feared by people. However, life is painful - what with wars, natural disasters, famines, and the burden of higher social classes. So is the peace of death not desirable ? A nihilistic cult can rise from any existing religion, and have a variety of origins. And it is both a destroyer of civilisations and a very seductive solace from the pains of the world.
Obviously, you can also have the clash of old (original) faiths and new faiths - religion is, like history, often decided by the victors, and a ruler can change a faith to further their own ends, which splits society and fosters resentment. Or a ruler is a zealot and enforces a rigid interpretation of the holy laws, creating religious resistance and heresies.