Question:

Why is a Vault CrossLink displaying the message: Source content for this CrossLink is not available? 

Answer:

This is working as expected. After creating a CrossLink document, a background service has to retrieve the rendition from the source document version. Refreshing the page or clicking the Re-sync with Source option from the CrossLink document's Action Menu resolves this issue. 

Related Documentation:

Vault CrossLink Administration Documentation: Configuring CrossLinks