To my knowledge, Phoenix doesn't support different client versions hitting one Phoenix server version. In other words, rolling upgrade isn't supported yet for 4.0, 4.1 & 4.2.x
As we get a distributed client base, I am wondering if there is room for different phoenix client and server versions to work together. This has accidentally worked in the past. Is there an official message here? For example, we plan on switching to the latest 4.2.X next week, but have folks who will have the 4.1 or 4.0 client versions. Will they work?