How to reproduce issue

  1. Install vim-plug:

    sh -c 'curl -fLo "${XDG_DATA_HOME:-$HOME/.local/share}"/nvim/site/autoload/plug.vim --create-dirs \
       https://raw.githubusercontent.com/junegunn/vim-plug/master/plug.vim'
    
  2. launch nvim:

    nvim
    
  3. Toggle fern into the screen:

    :Fern . -drawer -toggle
    
  4. Make session that will error:

    :mksession fern_opened.vim
    
  5. Makes session that will not error:

    :Fern . -drawer -toggle
    
    :mksession fern_closed.vim
    
  6. Close nvim:

    :q
    
  7. Open nvim:

    nvim
    
  8. Load session that won't show error:

    :source fern_closed.vim
    
  9. Load session that will error:

    :source fern_opened.vim