This comes from attempting to ingest a typical Citation object in the typical way. Strangely, it looks like the user can ingest one object without problems, but ingesting a second object immediately afterward results in the error. Coming back to it later allows her to ingest an object again successfully, but again the second one creates errors.
Some Citation objects are failing to ingest when the UUID setting is turned on, returning a "not found" error:
This comes from attempting to ingest a typical Citation object in the typical way. Strangely, it looks like the user can ingest one object without problems, but ingesting a second object immediately afterward results in the error. Coming back to it later allows her to ingest an object again successfully, but again the second one creates errors.