Unable to fetch Mailchimp campaign data, caught API exception: 500: Internal Server Error - A deep, internal error has occurred during the processing of your request. Please contact support.

Problem/Motivation

I get this message when the Campaign page loads:
Unable to fetch Mailchimp campaign data, caught API exception: 500: Internal Server Error - A deep, internal error has occurred during the processing of your request. Please contact support.
It will not list campaigns, so as a result, I cannot send the campaigns I create

Steps to reproduce

ddrush does show this error:
Warning The field Rendered item (rendered_item) on index
Default content index is missing view mode
configuration for some datasources or bundles. Review
(and re-save) the field settings.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes