diff --git a/.github/workflows/mutation.yml b/.github/workflows/mutation.yml
index df1db8d..7f71d5f 100644
--- a/.github/workflows/mutation.yml
+++ b/.github/workflows/mutation.yml
@@ -28,6 +28,7 @@ jobs:
         ['ubuntu-latest']
       php: >-
         ['8.3']
-      min-covered-msi: 100
+      min-msi: 100
+      threads: 1
     secrets:
       STRYKER_DASHBOARD_API_KEY: ${{ secrets.STRYKER_DASHBOARD_API_KEY }}
diff --git a/composer.json b/composer.json
index 3c7c8b1..00df417 100644
--- a/composer.json
+++ b/composer.json
@@ -64,6 +64,7 @@
     },
     "scripts": {
         "cs-fix": "php-cs-fixer fix",
+        "mutation": "roave-infection-static-analysis-plugin --min-msi=100",
         "rector": "rector",
         "test": "phpunit",
         "test-watch": "phpunit-watcher watch"
diff --git a/infection.json.dist b/infection.json.dist
index 9419316..7aedcac 100644
--- a/infection.json.dist
+++ b/infection.json.dist
@@ -16,6 +16,16 @@
             "ignoreSourceCodeByRegex": [
                 "\\$this->invalidateScriptCache.*"
             ]
+        },
+        "DecrementInteger": {
+            "ignoreSourceCodeByRegex": [
+                "mkdir\\(.*permissions: 0775.*"
+            ]
+        },
+        "IncrementInteger": {
+            "ignoreSourceCodeByRegex": [
+                "mkdir\\(.*permissions: 0775.*"
+            ]
         }
     }
 }
diff --git a/tests/AssignmentsStorageTest.php b/tests/AssignmentsStorageTest.php
index f2b2783..cd78b06 100644
--- a/tests/AssignmentsStorageTest.php
+++ b/tests/AssignmentsStorageTest.php
@@ -44,6 +44,21 @@ public function testGetFileUpdatedAtException(): void
         );
     }
 
+    public function testRemoveNonExistingDoesNotSaveFile(): void
+    {
+        $filePath = $this->getAssignmentsStorageFilePath();
+        $storage = new AssignmentsStorage($filePath);
+
+        touch($filePath, time() - 100);
+        clearstatcache();
+        $modifiedTimeBefore = filemtime($filePath);
+
+        $storage->remove(itemName: 'Operator', userId: 'john');
+
+        clearstatcache();
+        $this->assertSame($modifiedTimeBefore, filemtime($filePath));
+    }
+
     protected function createItemsStorage(): ItemsStorageInterface
     {
         return new ItemsStorage($this->getItemsStorageFilePath());
diff --git a/tests/AssignmentsStorageWithConcurrencyHandledTest.php b/tests/AssignmentsStorageWithConcurrencyHandledTest.php
index a8d9668..e0c7def 100644
--- a/tests/AssignmentsStorageWithConcurrencyHandledTest.php
+++ b/tests/AssignmentsStorageWithConcurrencyHandledTest.php
@@ -150,6 +150,21 @@ public function testRemoveByItemName(): void
         $this->assertEmpty($innerTestStorage->getByItemNames(['Accountant']));
     }
 
+    public function testNoReloadWhenTimestampIsUnchanged(): void
+    {
+        $filePath = $this->getAssignmentsStorageFilePath();
+        $innerStorage = new AssignmentsStorage($filePath, getFileUpdatedAt: static fn(): int => 12345);
+        $decorator = new ConcurrentAssignmentsStorageDecorator($innerStorage);
+
+        $decorator->add(new Assignment(userId: 'testUser', itemName: 'Researcher', createdAt: time()));
+
+        (new AssignmentsStorage($filePath))->add(
+            new Assignment(userId: 'testUser', itemName: 'Accountant', createdAt: time()),
+        );
+
+        $this->assertArrayNotHasKey('Accountant', $decorator->getByUserId('testUser'));
+    }
+
     protected function createItemsStorage(): ItemsStorageInterface
     {
         return new ConcurrentItemsStorageDecorator(new ItemsStorage($this->getItemsStorageFilePath()));
diff --git a/tests/ItemsStorage/ItemsStorageTest.php b/tests/ItemsStorage/ItemsStorageTest.php
index 2ce3011..03521ff 100644
--- a/tests/ItemsStorage/ItemsStorageTest.php
+++ b/tests/ItemsStorage/ItemsStorageTest.php
@@ -100,6 +100,36 @@ public function testLoadWithCustomGetFileUpdatedAt(): void
         $this->assertSame($time, $storage->get('test')->getCreatedAt());
     }
 
+    public function testRemoveChildNonExistingDoesNotSaveFile(): void
+    {
+        $filePath = $this->getItemsStorageFilePath();
+        $storage = new ItemsStorage($filePath);
+
+        touch($filePath, time() - 100);
+        clearstatcache();
+        $mtimeBefore = filemtime($filePath);
+
+        $storage->removeChild('posts.viewer', 'non-existing');
+
+        clearstatcache();
+        $this->assertSame($mtimeBefore, filemtime($filePath));
+    }
+
+    public function testRemoveChildrenNonExistingDoesNotSaveFile(): void
+    {
+        $filePath = $this->getItemsStorageFilePath();
+        $storage = new ItemsStorage($filePath);
+
+        touch($filePath, time() - 100);
+        clearstatcache();
+        $mtimeBefore = filemtime($filePath);
+
+        $storage->removeChildren('posts.view');
+
+        clearstatcache();
+        $this->assertSame($mtimeBefore, filemtime($filePath));
+    }
+
     public function testGetFileUpdatedAtException(): void
     {
         $this->expectException(RuntimeException::class);