Thanks @mara. I was able to track it down to my VM not being able to clone the websocket-driver-node.git. What I did was change the following:
In package.json, I changed line 18 from: "websocket-driver": "git://github.com/rstudio/websocket-driver-node.git#no-extensions"
to "websocket-driver": "https://github.com/rstudio/websocket-driver-node.git#no-extensions"
In package-lock.json, I changed line 2905 from: "version": "git://github.com/rstudio/websocket-driver-node.git#710ce3ed1bdc715e8afad6a257c8bfe9ae5ae358",
to "version": "https://github.com/rstudio/websocket-driver-node.git#710ce3ed1bdc715e8afad6a257c8bfe9ae5ae358",
Thanks for digging into this. shinyloadtest and proxyrec are still a WIP, feel free to open GH issues for any further problems.
For anyone else who comes across this thread, there are binaries available for proxyrec if you're on Linux or Mac. Instructions at: https://rstudio.github.io/shinyloadtest/