Customized download error

Sfc.ContentDownloadHandlerFactory implementation contains call to download operation

Above exception happens when VersionData is queried inside an Apex Class where Sfc.ContentDownloadHandlerFactory interface is used. 

To resolve the issue, avoid querying VersionData inside an Apex Class where Sfc.ContentDownloadHandlerFactory interface is used.

Querying VersionData isn’t allowed from the Download Handler. If a custom Apex download handler is active, this field is accessed from the API, and the download is not allowed, Salesforce will return a CONTENT_CUSTOMIZED_DOWNLOAD_EXCEPTION error.

Reference Article:

https://developer.salesforce.com/docs/atlas.en-us.api.meta/api/sforce_api_objects_contentversion.htm.