Has anyone had this problem before?
Theres nothing in the logs and I am on developer mode with debugging enabled.
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Create custom class & copy required functionality of vendor/magento/module-checkout/model/Session.php class file of Magento 2.3.3 version in it.
Then, use that custom class in Magento 2.3.4 version where you have added dependency of Magento\Checkout\Model\Session class file.
Or you can use '\Magento\Checkout\Model\Cart' class file to get all visible items of cart.