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

まず、macOS 10.15.5 上の MacVim 8.2.539 で問題を再現します。Ruby バッファーを表示した状態でコンピューターをスリープさせてから復帰させ、その後、影響を受けた split またはタブを set filetype=ruby と比較します。スリープ／復帰後、および OS がウィンドウを移動したり外部モニターを再接続したりした後も、構文ハイライトを利用できれば完了です。