DSpace 6.3 SWORDv2 503 Backend Error - Debugging Hints?

[Ray W]

Hi Everyone,

Has anyone encountered the following error while ingesting a SWORDv2 deposit? 

Unable to retrieve service document: Server responded with HTTP code 503: "Backend fetch failed" 

A user has reported it and we cannot reproduce. I checked logs and I don't see any clues there. The strange part is we are able to ingest via SWORDv2 items into the same collection (and multiple other ones) as the user. Should we consider investigating the SWORDv2 client they may be using? Perhaps on their end something is misconfigured? Any suggestions would be appreciated, thank you for your time.

Best,

Ray