Today I learned that the API Call for SIS Import Errors, doesn't included imports with a workflow status of "failed". If it has a workflow of "imported_with_messages" or "failed_with_messages" they are included, but just "failed" is not.
According to Canvas Support this is expected behavior, but it is unclear to me why a workflow_status of "failed" wouldn't be included in the errors report, but "failed_with_messages" would be included.
When I saw multiple errors get reported as "imported_with_messages", it was unclear to me why they were failing. However, after looking through the complete list of imports, I discovered the source of the problem was a workflow_state of "failed" that didn't appear on the error report.
Therefore, I am suggesting that the SIS Import Errors report includes SIS Imports with a workflow_status of "failed"