Stablize register user spec

qa/qa/resource/user.rb

@@ -98,6 +98,12 @@ module QA
         super
       end
 
+      def exists?
+        api_get
+      rescue ResourceNotFoundError
+        false
+      end
+
       def api_delete
         super
 

qa/qa/specs/features/browser_ui/1_manage/login/register_spec.rb

@@ -64,6 +64,7 @@ module QA
             Page::Profile::Accounts::Show.perform do |show|
               show.delete_account(user.password)
             end
+            Support::Waiter.wait_until { !user.exists? }
           end
 
           it 'allows recreating with same credentials', testcase: 'https://gitlab.com/gitlab-org/gitlab/-/quality/test_cases/347868' do
@@ -83,7 +84,7 @@ module QA
           end
 
           after do
-            @recreated_user.remove_via_api!
+            @recreated_user&.remove_via_api!
           end
 
           def admin_api_client