--- a/.emacs-my	Tue Oct 13 20:51:39 2020 +0300
+++ b/.emacs-my	Tue Oct 13 21:24:58 2020 +0300
@@ -2565,6 +2565,9 @@
 ;; (defun my-diff-auto-refine-mode-on () (diff-auto-refine-mode 1))
 ;; (add-hook 'diff-mode-hook 'my-diff-auto-refine-mode-on)
 
+;; Since 27.1 it is enabled during font-lock. Need to disable explicitly.
+(setq diff-refine nil)
+
 (when (and window-system (< emacs-major-version 26))
   (my--eval-after-load diff-mode
     (set-face-foreground 'diff-added "DarkGreen")