Julia was not working in JupyterLab for some reason. I fixed this by following the advice here, here (run which jupyter in command line to get the path, which you'll use in the next step, and here (run in the Julia prompt ENV["JUPYTER"]= "PATH-FROM-PREVIOUS-STEP", replacing PATH-FROM-PREVIOUS-STEP with the path from the previous step, then run Pkg.build("IJulia")).

IJulia would not precompile.