diff -Naur a/vendor/magento/module-catalog/Model/Product/ProductFrontendAction/Synchronizer.php b/vendor/magento/module-catalog/Model/Product/ProductFrontendAction/Synchronizer.php
--- a/vendor/magento/module-catalog/Model/Product/ProductFrontendAction/Synchronizer.php
+++ b/vendor/magento/module-catalog/Model/Product/ProductFrontendAction/Synchronizer.php
@@ -16,6 +16,8 @@
 use Magento\Framework\EntityManager\EntityManager;

 /**
+ * A Product Widget Synchronizer.
+ *
  * Service which allows to sync product widget information, such as product id with db. In order to reuse this info
  * on different devices
  */
@@ -85,9 +87,10 @@ public function __construct(
     }

     /**
-     * Find lifetime in configuration. Configuration is hold in Stores Configuration
-     * Also this configuration is generated by:
-     * @see \Magento\Catalog\Model\Widget\RecentlyViewedStorageConfiguration
+     * Finds lifetime in configuration.
+     *
+     * Configuration is hold in Stores Configuration. Also this configuration is generated by
+     * {@see Magento\Catalog\Model\Widget\RecentlyViewedStorageConfiguration}
      *
      * @param string $namespace
      * @return int
@@ -108,6 +111,8 @@ private function getLifeTimeByNamespace($namespace)
     }

     /**
+     * Filters actions.
+     *
      * In order to avoid suspicious actions, we need to filter them in DESC order, and slice only items that
      * can be persisted in database.
      *
@@ -138,7 +143,9 @@ private function getProductIdsByActions(array $actions)
         $productIds = [];

         foreach ($actions as $action) {
-            $productIds[] = $action['product_id'];
+            if (isset($action['product_id']) && is_int($action['product_id'])) {
+                $productIds[] = $action['product_id'];
+            }
         }

         return $productIds;
@@ -159,33 +166,37 @@ public function syncActions(array $productsData, $typeId)
         $customerId = $this->session->getCustomerId();
         $visitorId = $this->visitor->getId();
         $collection = $this->getActionsByType($typeId);
-        $collection->addFieldToFilter('product_id', $this->getProductIdsByActions($productsData));
-
-        /**
-         * Note that collection is also filtered by visitor id and customer id
-         * This collection shouldn't be flushed when visitor has products and then login
-         * It can remove only products for visitor, or only products for customer
-         *
-         * ['product_id' => 'added_at']
-         * @var ProductFrontendActionInterface $item
-         */
-        foreach ($collection as $item) {
-            $this->entityManager->delete($item);
-        }
-
-        foreach ($productsData as $productId => $productData) {
-            /** @var ProductFrontendActionInterface $action */
-            $action = $this->productFrontendActionFactory->create([
-                'data' => [
-                    'visitor_id' => $customerId ? null : $visitorId,
-                    'customer_id' => $this->session->getCustomerId(),
-                    'added_at' => $productData['added_at'],
-                    'product_id' => $productId,
-                    'type_id' => $typeId
-                ]
-            ]);
-
-            $this->entityManager->save($action);
+        $productIds = $this->getProductIdsByActions($productsData);
+
+        if ($productIds) {
+            $collection->addFieldToFilter('product_id', $productIds);
+
+            /**
+             * Note that collection is also filtered by visitor id and customer id
+             * This collection shouldn't be flushed when visitor has products and then login
+             * It can remove only products for visitor, or only products for customer
+             *
+             * ['product_id' => 'added_at']
+             * @var ProductFrontendActionInterface $item
+             */
+            foreach ($collection as $item) {
+                $this->entityManager->delete($item);
+            }
+
+            foreach ($productsData as $productId => $productData) {
+                /** @var ProductFrontendActionInterface $action */
+                $action = $this->productFrontendActionFactory->create([
+                    'data' => [
+                        'visitor_id' => $customerId ? null : $visitorId,
+                        'customer_id' => $this->session->getCustomerId(),
+                        'added_at' => $productData['added_at'],
+                        'product_id' => $productId,
+                        'type_id' => $typeId
+                    ]
+                ]);
+
+                $this->entityManager->save($action);
+            }
         }
     }

diff -Naur a/vendor/magento/framework/DB/Adapter/Pdo/Mysql.php b/vendor/magento/framework/DB/Adapter/Pdo/Mysql.php
--- a/vendor/magento/framework/DB/Adapter/Pdo/Mysql.php
+++ b/vendor/magento/framework/DB/Adapter/Pdo/Mysql.php
@@ -2955,7 +2955,7 @@ class Mysql extends \Zend_Db_Adapter_Pdo_Mysql implements AdapterInterface
                 if (isset($condition['to'])) {
                     $query .= empty($query) ? '' : ' AND ';
                     $to     = $this->_prepareSqlDateCondition($condition, 'to');
-                    $query = $this->_prepareQuotedSqlCondition($query . $conditionKeyMap['to'], $to, $fieldName);
+                    $query = $query . $this->_prepareQuotedSqlCondition($conditionKeyMap['to'], $to, $fieldName);
                 }
             } elseif (array_key_exists($key, $conditionKeyMap)) {
                 $value = $condition[$key];