Syntax highlight is lost after sleep

Describe the bug

I believe this only happens with the currently visible tab, in whatever split has the cursor. If no split then the tab's current buffer.

To Reproduce
Put the computer to sleep. Wake the computer. Text is now all white. set filetype=ruby (or whatever) fixes it. Happens almost every time.

I have suspicions that this may be related to macOS moving the windows around as the external monitors are recognized.

Expected behavior
Syntax highlighting should never be lost as a result of a sleep/wake cycle or as a result of the OS moving the window.

Environment (please complete the following information):

• Vim version (see below)
• OS: macOs 10.15.5
• Terminal: GUI - MacVim 8.2.539 (163)

VIM - Vi IMproved 8.1 (2018 May 18, compiled Apr 17 2020 17:49:10)
macOS version
Included patches: 1-503, 505-680, 682-2292
Compiled by root@apple.com
Normal version without GUI.  Features included (+) or not (-):
+acl               -farsi             -mouse_sysmouse    -tag_any_white
-arabic            +file_in_path      -mouse_urxvt       -tcl
+autocmd           +find_in_path      +mouse_xterm       -termguicolors
+autochdir         +float             +multi_byte        +terminal
-autoservername    +folding           +multi_lang        +terminfo
-balloon_eval      -footer            -mzscheme          +termresponse
-balloon_eval_term +fork()            +netbeans_intg     +textobjects
-browse            -gettext           +num64             +textprop
+builtin_terms     -hangul_input      +packages          +timers
+byte_offset       +iconv             +path_extra        +title
+channel           +insert_expand     -perl              -toolbar
+cindent           +job               +persistent_undo   +user_commands
-clientserver      +jumplist          +postscript        -vartabs
+clipboard         -keymap            +printer           +vertsplit
+cmdline_compl     +lambda            -profile           +virtualedit
+cmdline_hist      -langmap           +python/dyn        +visual
+cmdline_info      +libcall           -python3           +visualextra
+comments          +linebreak         +quickfix          +viminfo
-conceal           +lispindent        +reltime           +vreplace
+cryptv            +listcmds          -rightleft         +wildignore
+cscope            +localmap          +ruby/dyn          +wildmenu
+cursorbind        -lua               +scrollbind        +windows
+cursorshape       +menu              +signs             +writebackup
+dialog_con        +mksession         +smartindent       -X11
+diff              +modify_fname      -sound             -xfontset
+digraphs          +mouse             +spell             -xim
-dnd               -mouseshape        +startuptime       -xpm
-ebcdic            -mouse_dec         +statusline        -xsmp
-emacs_tags        -mouse_gpm         -sun_workshop      -xterm_clipboard
+eval              -mouse_jsbterm     +syntax            -xterm_save
+ex_extra          -mouse_netterm     +tag_binary
+extra_search      +mouse_sgr         -tag_old_static
   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/share/vim"
Compilation: gcc -c -I. -Iproto -DHAVE_CONFIG_H   -DMACOS_X_UNIX  -g -O2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1
Linking: gcc   -L/usr/local/lib -o vim        -lm -lncurses  -liconv -framework Cocoa

Start by reproducing the issue in MacVim 8.2.539 on macOS 10.15.5: sleep and wake the computer with a Ruby buffer visible, then compare the affected split or tab with set filetype=ruby. Done means syntax highlighting remains available after sleep/wake and after the OS moves windows or reconnects external monitors.