If you're like me, you prefer to keep things updated as often as possible. Besides, keeping things updated is a part of preventing security breaches and taking advantage of bug fixes. Unfortunately, this can cause a headache with Magento 2. The issue Magento 2 fails to load and reports 1 exception(s):Exception #0 (Exception): Deprecated Functionality:...

The fix to this issue is because the form key validation is missing on check out. You can view the fix here How to fix Magento checkout after upgrading