Added getScopeCacheKey in order to define the right cache key based on store ID

app/code/Magento/Catalog/Model/CategoryRepository.php

@@ -7,10 +7,12 @@
 
 namespace Magento\Catalog\Model;
 
+use Magento\Catalog\Api\Data\CategoryInterface;
 use Magento\Framework\Exception\CouldNotSaveException;
 use Magento\Framework\Exception\NoSuchEntityException;
+use Magento\Framework\Exception\SerializationException;
 use Magento\Framework\Exception\StateException;
-use Magento\Catalog\Api\Data\CategoryInterface;
+use Magento\Framework\Phrase;
 
 /**
  * Repository for categories.
@@ -128,10 +130,12 @@ public function save(\Magento\Catalog\Api\Data\CategoryInterface $category)
 
     /**
      * @inheritdoc
+     *
+     * @throws SerializationException
      */
     public function get($categoryId, $storeId = null)
     {
-        $cacheKey = $storeId ?? 'all';
+        $cacheKey = $this->getScopeCacheKey($storeId);
         if (!isset($this->instances[$categoryId][$cacheKey])) {
             /** @var Category $category */
             $category = $this->categoryFactory->create();
@@ -238,4 +242,26 @@ private function getMetadataPool()
         }
         return $this->metadataPool;
     }
+
+    /**
+     * Returns a cache key based on scope
+     *
+     * @param string|int|null $storeId
+     *
+     * @throws SerializationException
+     * @return int|string
+     */
+    private function getScopeCacheKey($storeId = null)
+    {
+        if (null !== $storeId && !is_numeric($storeId)) {
+            throw new SerializationException(
+                new Phrase(
+                    'The "%value" value\'s type is invalid. The "%type" type was expected. '
+                    . 'Verify and try again.',
+                    ['value' => $storeId, 'type' => 'int']
+                )
+            );
+        }
+        return $storeId === null ? 'all' : (int)$storeId;
+    }
 }

dev/tests/integration/testsuite/Magento/Catalog/Model/CategoryRepositoryTest.php

@@ -12,6 +12,7 @@
 use Magento\Catalog\Model\ResourceModel\Category\CollectionFactory as CategoryCollectionFactory;
 use Magento\Catalog\Model\ResourceModel\Product\CollectionFactory;
 use Magento\Framework\Exception\LocalizedException;
+use Magento\Store\Model\StoreFactory;
 use Magento\TestFramework\Catalog\Model\CategoryLayoutUpdateManager;
 use Magento\TestFramework\Helper\Bootstrap;
 use PHPUnit\Framework\TestCase;
@@ -46,6 +47,11 @@ class CategoryRepositoryTest extends TestCase
      */
     private $categoryCollectionFactory;
 
+    /**
+     * @var StoreFactory
+     */
+    private $storeFactory;
+
     /**
      * Sets up common objects.
      *
@@ -57,6 +63,7 @@ protected function setUp()
         $this->layoutManager = Bootstrap::getObjectManager()->get(CategoryLayoutUpdateManager::class);
         $this->productCollectionFactory = Bootstrap::getObjectManager()->get(CollectionFactory::class);
         $this->categoryCollectionFactory = Bootstrap::getObjectManager()->create(CategoryCollectionFactory::class);
+        $this->storeFactory = Bootstrap::getObjectManager()->create(StoreFactory::class);
     }
 
     /**
@@ -151,14 +158,14 @@ public function testGetCategoryForProvidedStore()
 
         $categoryFirstStore = $categoryRepository->get(
             self::FIXTURE_TWO_STORES_CATEGORY_ID,
-            self::FIXTURE_FIRST_STORE_CODE
+            $this->storeFactory->create()->load(self::FIXTURE_FIRST_STORE_CODE)->getId()
         );
 
         $this->assertSame('category-defaultstore', $categoryFirstStore->getUrlKey());
 
         $categorySecondStore = $categoryRepository->get(
             self::FIXTURE_TWO_STORES_CATEGORY_ID,
-            self::FIXTURE_SECOND_STORE_CODE
+            $this->storeFactory->create()->load(self::FIXTURE_SECOND_STORE_CODE)->getId()
         );
 
         $this->assertSame('category-fixturestore', $categorySecondStore->getUrlKey());