When you redirect a customer who is logged in to the login form, Magento automatically redirects the customer to their dashboard.
In your code, you need to log the customer out first; then you can redirect them to the login form.
Sorry, I can't read sometimes.
I think you're running into a caching problem. You don't write where you execute the code, but ...
You can write on breadcrumb.phtml page By Objectmanager like this :
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$request = $objectManager->get('\Magento\Framework\App\Request\Http');
$customerSession = $objectManager->get('Magento\Customer\Model\Session');
From the login page , somehow your code reaches to this controller page (file: /vendor/magento/module-customer/Controller/Account/LoginPost.php), here you will see that message , then you can edit here or in your custom module.
EditI checked your case , so in your case this file will be present in your custom module, override is given already by you , you ...