MC-18144: Full page cache issue with non-default store view

Author: Roman Lytvynenko

app/code/Magento/Store/App/Action/Plugin/Context.php

@@ -137,7 +137,7 @@ private function updateContext(StoreInterface $store)
         $this->httpContext->setValue(
             StoreManagerInterface::CONTEXT_STORE,
             $store->getCode(),
-            $store->isUseStoreInUrl() ? $store->getCode() : $this->storeManager->getDefaultStoreView()->getCode()
+            $store->isUseStoreInUrl() ? $store->getCode() : $defaultStore->getCode()
         );
 
         $this->httpContext->setValue(