The Mormon church is going through a very similar thing. I heard a comment from a prominent lds podcaster John Delin ( I love that guy) that the Mormon doctrine as it presently stands is not sustainable long term. It needs repaid reform if it’s to survive long term.
Interestingly I have actually attended a Christadelphian church. I was shocked, to learn, that I could used terms and doctrine, that I thought was specific to the JWs, and they knew exactly what I was talking about. Just for the record the JWs did not develop out of christadelphianisim but out of Millerite advetistisim.