Communication Failure is displayed when trying to swap an image in a section of the email
This is known to occur when the email contains a significant amount of elements configured with dynamic content. These elements refer to subject, hero-banner, cta-button, etc.
For example, for an email that contains 10 elements with 50 segments (used for dynamic content), there are at least 500 versions (i.e. 10 elements multiplied by 50 segments) of the email that needs to be updated when an element is updated (e.g. swapping an image)
In order to avoid the communication failure or be able to swap an image, it is recommended to reduce the number of elements configured with dynamic content (i.e. make some elements static where possible)