There is a change to the experimental API For getting default values for a custom field.
Get custom field context default values REST API has been updated to return the correct value.
The contextId does not match the contextId returned from the Issue custom field contexts REST API, despite both returning data for the same custom field.
The contextId for custom fields should be consistent across API’s so they can be used to build a complete snapshot of a custom field.
Developers should be aware that the Get custom field context default values REST API will now return the correct contextId and will match the Get custom field contexts API.