The wrong InputStreamReader is being imported here:
https://github.com/Chisel-Team/Chisel/blob/1.9/dev/src/main/java/team/chisel/client/render/ModelLoaderChisel.java#L7

This is an issue that is present across all branches that I have seen. The reason that this wasn't reported by anyone sooner is that jLine (the library that is being imported from) is present on the client even though the library is marked as server-only. I have an environment where I do not load jLine on the client, hence the crash.