We are having an issue where our custom Lightning components that were developed, fully tested, and working using the new Salesforce Locker Service security requirements with Locker Service enabled in Winter '17 and Spring '17 APIs versions 38.0 and 39.0 have all broken when upgraded to the new Summer '17 API 40.0 Locker Service enforcement.

What is the difference between enabling Locker Service for the Winter '17 and Spring '17 releases and the new Summer '17 enforcement in API version 40.0?

I can't seem to find any documentation that explains the difference in the security requirements between the two, only documentation on what is required for Locker Service, which hasn't changed since it was initially released last year. This is the documentation we used to prepare for Locker Services: https://developer.salesforce.com/blogs/developer-relations/2016/04/introducing-lockerservice-lightning-components.html

Here are the errors we are receiving, any insight would be much appreciated as these errors are extremely vague and do not directly reference our component markup:
Uncaught render threw an error in 'markup://aura:html' [Failed to execute 'appendChild' on 'Node': parameter 1 is not of type 'Node'.]
AND
Uncaught render threw an error in 'markup://aura:expression' [Assertion Failed!: Descriptor for Config required for registration : undefined]

Thanks,
Mai