Don't save user in socket, just save the name.

lib/pleroma/web/channels/user_socket.ex

@@ -25,7 +25,7 @@ defmodule Pleroma.Web.UserSocket do
   def connect(%{"token" => token}, socket) do
     with {:ok, user_id} <- Phoenix.Token.verify(socket, "user socket", token, max_age: 84600),
          %User{} = user <- Pleroma.Repo.get(User, user_id) do
-      {:ok, assign(socket, :user, user)}
+      {:ok, assign(socket, :user_name, user.nickname)}
     else
       _e -> :error
     end