diff --git a/app/workers/work_packages/apply_working_days_change_job.rb b/app/workers/work_packages/apply_working_days_change_job.rb
index ddee93e1ca..97370b00b7 100644
--- a/app/workers/work_packages/apply_working_days_change_job.rb
+++ b/app/workers/work_packages/apply_working_days_change_job.rb
@@ -44,20 +44,32 @@ class WorkPackages::ApplyWorkingDaysChangeJob < ApplicationJob
   def each_applicable_work_package
     WorkPackage
       .where(ignore_non_working_days: false)
-      .order(start_date: :asc)
+      .where.not(start_date: nil, due_date: nil)
+      .order(WorkPackage.arel_table[:start_date].asc.nulls_first,
+             WorkPackage.arel_table[:due_date].asc)
       .pluck(:id)
       .each do |id|
         work_package = WorkPackage.find(id)
-        next if dates_and_duration_match?(work_package)
+        next unless dates_and_duration_mismatch?(work_package)
 
         yield work_package
       end
   end
 
-  def dates_and_duration_match?(work_package)
-    days.working?(work_package.start_date) \
-      && days.working?(work_package.due_date) \
-      && days.duration(work_package.start_date, work_package.due_date) == work_package.duration
+  def dates_and_duration_mismatch?(work_package)
+    # precondition: ignore_non_working_days is false
+    non_working?(work_package.start_date) \
+      || non_working?(work_package.due_date) \
+      || wrong_duration?(work_package)
+  end
+
+  def non_working?(date)
+    date && !days.working?(date)
+  end
+
+  def wrong_duration?(work_package)
+    computed_duration = days.duration(work_package.start_date, work_package.due_date)
+    computed_duration && work_package.duration != computed_duration
   end
 
   def days
diff --git a/spec/workers/work_packages/apply_working_days_change_job_spec.rb b/spec/workers/work_packages/apply_working_days_change_job_spec.rb
index d19c19df4b..0c0a624cec 100644
--- a/spec/workers/work_packages/apply_working_days_change_job_spec.rb
+++ b/spec/workers/work_packages/apply_working_days_change_job_spec.rb
@@ -42,9 +42,13 @@ RSpec.describe WorkPackages::ApplyWorkingDaysChangeJob do
   end
 
   context 'when a work package includes a date that is now a non-working day' do
-    let_schedule(<<~CHART, ignore_non_working_days: false)
-      days          | MTWTFSS |
-      work_package  | XXXX    |
+    let_schedule(<<~CHART)
+      days                  | MTWTFSS |
+      work_package          | XXXX    |
+      work_package_on_start |   XX    |
+      work_package_on_due   | XXX     |
+      wp_start_only         |   [     |
+      wp_due_only           |   ]     |
     CHART
 
     before do
@@ -53,14 +57,59 @@ RSpec.describe WorkPackages::ApplyWorkingDaysChangeJob do
 
     it 'moves the finish date to the corresponding number of now-excluded days to maintain duration [#31992]' do
       job.perform_now(user_id: user.id)
+      expect(WorkPackage.all).to match_schedule(<<~CHART)
+        days                  | MTWTFSS |
+        work_package          | XX.XX   |
+        work_package_on_start |    XX   |
+        work_package_on_due   | XX.X    |
+        wp_start_only         |    [    |
+        wp_due_only           |    ]    |
+      CHART
+    end
+  end
+
+  context 'when a work package was scheduled to start on a date that is now a non-working day' do
+    let_schedule(<<~CHART)
+      days          | MTWTFSS |
+      work_package  |   XX    |
+    CHART
+
+    before do
+      set_non_working_week_days('wednesday')
+    end
+
+    it 'moves the start date to the earliest working day in the future, ' \
+       'and the finish date changes by consequence [#31992]' do
+      job.perform_now(user_id: user.id)
       expect(WorkPackage.all).to match_schedule(<<~CHART)
         days         | MTWTFSS |
-        work_package | XX.XX   |
+        work_package |    XX   |
       CHART
     end
   end
 
-  context 'when a work package includes a date that is now a non-working day, but has working days include weekends' do
+  context 'when a follower has a predecessor with dates covering a day that is now a non-working day' do
+    let_schedule(<<~CHART)
+      days        | MTWTFSS |
+      predecessor |  XX     | working days work week
+      follower    |    XXX  | working days include weekends, follows predecessor
+    CHART
+
+    before do
+      set_non_working_week_days('wednesday')
+    end
+
+    it 'moves the follower start date by consequence of the predecessor dates shift [#31992]' do
+      job.perform_now(user_id: user.id)
+      expect(WorkPackage.all).to match_schedule(<<~CHART)
+        days        | MTWTFSS |
+        predecessor |  X.X    | working days work week
+        follower    |     XXX | working days include weekends
+      CHART
+    end
+  end
+
+  context 'when a work package has working days include weekends, and includes a date that is now a non-working day' do
     let_schedule(<<~CHART)
       days          | MTWTFSS |
       work_package  | XXXX    | working days include weekends
@@ -79,35 +128,24 @@ RSpec.describe WorkPackages::ApplyWorkingDaysChangeJob do
     end
   end
 
-  context 'when having multiple work packages' do
-    let_schedule(<<~CHART, ignore_non_working_days: false)
-      days | MTWTFSS |
-      wp1  | XX      |
-      wp2  |  XX     |
-      wp3  |   XX    |
-      wp4  |    XX   |
-      wp5  | XXXXX   |
+  context 'when a work package only has a duration' do
+    let_schedule(<<~CHART)
+      days          | MTWTFSS |
+      work_package  |         | duration 3 days
     CHART
 
     before do
       set_non_working_week_days('wednesday')
     end
 
-    it 'updates all impacted work packages' do
+    it 'does not change anything' do
       job.perform_now(user_id: user.id)
-      expect(WorkPackage.all).to match_schedule(<<~CHART)
-        days | MTWTFSS  |
-        wp1  | XX       |
-        wp2  |  X.X     |
-        wp3  |    XX    |
-        wp4  |    XX    |
-        wp5  | XX.XX..X |
-      CHART
+      expect(work_package.duration).to eq(3)
     end
   end
 
   context 'when having multiple work packages following each other' do
-    let_schedule(<<~CHART, ignore_non_working_days: false)
+    let_schedule(<<~CHART)
       days | MTWTFSS   |
       wp1  |     X..XX | follows wp2
       wp2  |    X      | follows wp3
@@ -132,43 +170,28 @@ RSpec.describe WorkPackages::ApplyWorkingDaysChangeJob do
     end
   end
 
-  context 'when a work package was scheduled to start on a date that is now a non-working day' do
-    let_schedule(<<~CHART, ignore_non_working_days: false)
-      days          | MTWTFSS |
-      work_package  |   XX    |
-    CHART
-
-    before do
-      set_non_working_week_days('wednesday')
-    end
-
-    it 'moves the start date to the earliest working day in the future, ' \
-       'and the finish date changes by consequence [#31992]' do
-      job.perform_now(user_id: user.id)
-      expect(WorkPackage.all).to match_schedule(<<~CHART)
-        days         | MTWTFSS |
-        work_package |    XX   |
-      CHART
-    end
-  end
-
-  context 'when a follower has a predecessor with dates covering a day that is now a non-working day' do
+  context 'when having multiple work packages following each other and first one only has a due date' do
     let_schedule(<<~CHART)
-      days        | MTWTFSS |
-      predecessor |  XX     | working days work week
-      follower    |    XXX  | working days include weekends, follows predecessor
+      days | MTWTFSS   |
+      wp1  |     X..XX | follows wp2
+      wp2  |   XX      | follows wp3
+      wp3  |  ]       |
     CHART
 
     before do
-      set_non_working_week_days('wednesday')
+      set_non_working_week_days('tuesday', 'wednesday', 'friday')
     end
 
-    it 'moves the follower start date by consequence of the predecessor dates shift [#31992]' do
-      job.perform_now(user_id: user.id)
+    it 'updates them only once' do
+      expect { job.perform_now(user_id: user.id) }
+        .to change { WorkPackage.pluck(:lock_version) }
+        .from([0, 0, 0])
+        .to([1, 1, 1])
       expect(WorkPackage.all).to match_schedule(<<~CHART)
-        days        | MTWTFSS |
-        predecessor |  X.X    | working days work week
-        follower    |     XXX | working days include weekends
+        days | MTWTFSSm  t ssm  t ssm |
+        wp1  |               X..X...X |
+        wp2  |        X..X            |
+        wp3  |    ]                   |
       CHART
     end
   end