Only update when fields actually changed.

ee/app/services/epics/update_service.rb

 module Epics
   class UpdateService < Epics::BaseService
+    EPIC_DATE_FIELDS = %I[
+      start_date_fixed
+      start_date_is_fixed
+      due_date_fixed
+      due_date_is_fixed
+    ].freeze
+
     def execute(epic)
       # start_date and end_date columns are no longer writable by users because those
       # are composite fields managed by the system.
@@ -7,9 +14,7 @@ module Epics
 
       update(epic)
 
-      if (params.keys.map(&:to_sym) & [:start_date_fixed, :start_date_is_fixed, :due_date_fixed, :due_date_is_fixed]).present?
-        epic.update_start_and_due_dates
-      end
+      epic.update_start_and_due_dates if have_epic_dates_changed?(epic)
 
       epic
     end
@@ -25,5 +30,11 @@ module Epics
 
       todo_service.update_epic(epic, current_user, old_mentioned_users)
     end
+
+    private
+
+    def have_epic_dates_changed?(epic)
+      (epic.previous_changes.keys.map(&:to_sym) & EPIC_DATE_FIELDS).present?
+    end
   end
 end