Why did my binary fields stop syncing?

Resolution

Binary data fields, such as the Body of an Attachment object, are unsupported by Heroku Connect.

Specifically, the Bulk API used to communicate with Salesforce at high volume doesn't support encoding binary data, even though the SOAP API, used for lower-traffic changes, does support it. Therefore, you may have a binary data field successfully syncing for a while using SOAP, but once your data change volume reaches the point where Heroku Connect switches to the Bulk API, this field will no longer sync successfully.