Syntax error when opening Vim if the Startify screen was the last open buffer

If the Startify screen was the last buffer I closed, when I start Vim, I see these errors:

Error detected while processing /Users/bz/.vim/plugged/vim-startify/syntax/startify.vim:
line   31:
E121: Undefined variable: g:startify_header
Press ENTER or type command to continue
Error detected while processing /Users/bz/.vim/plugged/vim-startify/syntax/startify.vim:
line   31:
E116: Invalid arguments for function len(g:startify_header) + 2) .'l/'

And then Vim opens what looks like an empty buffer.

When I try to go to the Startify screen with :Startify, I see:

Error detected while processing function startify#insane_in_the_membrane:
line   49:
E21: Cannot make changes, 'modifiable' is off
Press ENTER or type command to continue

Which seems related to https://github.com/mhinz/vim-startify/issues/406.

I can however get back to the Startify screen if I use :SClose.

Also no errors when the last buffer I close is another file.

VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Jan  8 2020 00:57:48)
macOS version
Included patches: 1-100
Compiled by Homebrew
Huge version without GUI.  Features included (+) or not (-):
+acl               -farsi             -mouse_sysmouse    -tag_old_static
+arabic            +file_in_path      +mouse_urxvt       -tag_any_white
+autocmd           +find_in_path      +mouse_xterm       -tcl
+autochdir         +float             +multi_byte        +termguicolors
-autoservername    +folding           +multi_lang        +terminal
-balloon_eval      -footer            -mzscheme          +terminfo
+balloon_eval_term +fork()            +netbeans_intg     +termresponse
-browse            +gettext           +num64             +textobjects
++builtin_terms    -hangul_input      +packages          +textprop
+byte_offset       +iconv             +path_extra        +timers
+channel           +insert_expand     +perl              +title
+cindent           +job               +persistent_undo   -toolbar
-clientserver      +jumplist          +popupwin          +user_commands
+clipboard         +keymap            +postscript        +vartabs
+cmdline_compl     +lambda            +printer           +vertsplit
+cmdline_hist      +langmap           +profile           +virtualedit
+cmdline_info      +libcall           -python            +visual
+comments          +linebreak         +python3           +visualextra
+conceal           +lispindent        +quickfix          +viminfo
+cryptv            +listcmds          +reltime           +vreplace
+cscope            +localmap          +rightleft         +wildignore
+cursorbind        +lua               +ruby              +wildmenu
+cursorshape       +menu              +scrollbind        +windows
+dialog_con        +mksession         +signs             +writebackup
+diff              +modify_fname      +smartindent       -X11
+digraphs          +mouse             -sound             -xfontset
-dnd               -mouseshape        +spell             -xim
-ebcdic            +mouse_dec         +startuptime       -xpm
+emacs_tags        -mouse_gpm         +statusline        -xsmp
+eval              -mouse_jsbterm     -sun_workshop      -xterm_clipboard
+ex_extra          +mouse_netterm     +syntax            -xterm_save
+extra_search      +mouse_sgr         +tag_binary
   system vimrc file: "$VIM/vimrc"
     user vimrc file: "$HOME/.vimrc"
 2nd user vimrc file: "~/.vim/vimrc"
      user exrc file: "$HOME/.exrc"
       defaults file: "$VIMRUNTIME/defaults.vim"
  fall-back for $VIM: "/usr/local/share/vim"
Compilation: clang -c -I. -Iproto -DHAVE_CONFIG_H   -DMACOS_X -DMACOS_X_DARWIN  -g -O2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1
Linking: clang   -L. -fstack-protector-strong -L/usr/local/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/openssl@1.1/lib -L/usr/local/opt/readline/lib  -L/usr/local/lib -o vim        -lncurses -liconv -lintl -framework AppKit  -L/usr/local/opt/lua/lib -llua5.3 -mmacosx-version-min=10.14 -fstack-protector-strong -L/usr/local/lib  -L/usr/local/Cellar/perl/5.30.1/lib/perl5/5.30.1/darwin-thread-multi-2level/CORE -lperl -lm -lutil -lc  -L/usr/local/opt/python/Frameworks/Python.framework/Versions/3.7/lib/python3.7/config-3.7m-darwin -lpython3.7m -framework CoreFoundation  -lruby.2.6

mhinz / vim-startify

Syntax error when opening Vim if the Startify screen was the last open buffer #408