Error (websocket): in callback `on-message': File error: "Couldn't find command to check if file exists"

[indigoviolet]

I've started having this error recently. If it matters, this is Jupyter notebook running on a remote server. Happy to provide more debugging information if I can.

This error leads to the buffer in emacs being empty, but I noticed that if I type text in to the browser textarea, it does show up in the buffer -- so they are connected.