Missing attachments in Confluence after migrating via Assistant

Issue Summary

Some customers are facing a problem when migrating space via Confluence Migration assistant after the migration is successfully completed some attachments are missing in the destination Cloud site.

Steps to Reproduce

1. Migrate spaces using CCMA
2. Verify the pages
3. Random pages will be missing attachments

Expected Results

The Assistant would fail to migrate that particular space, forcing a re-migration for that particular space.

Actual Results

The spaces are migrated successfully, even if the assistant failed to read an attachment.

The below exception is thrown in the atlassian-confluence.log file:

com.atlassian.migration.agent.service.stepexecutor.attachment.AttachmentDataProvider$AttachmentDataRetrievalException: Could not get attachment 289965820 data
.....

You should see several of those exceptions in the logs.

Workaround

Remigrate the affected spaces or manually upload the files to the destination pages.

You might need to clear out the MIG_ATTACHMENT table on your server to avoid previous results to interfere in your next runs.

1. Shutdown Confluence
2. Access your database
3. Run

DELETE FROM MIG_ATTACHMENT;

This table is specific of the Migration Assistant, and it records the attachments migration.