Since your question is pretty vague, these possible causes may provide a clue. If you want more detailed feedback, please provide some details about your document (or post the document), your reload strategy, your server setup and what investigations you already did yourself.
- Environment differences causing some document elements to be absent (scripts, files, qvd's, other source files)
- Different data load / data source causing the expected values to be absent
- Data reduction (section access) causing the expected values to be eliminated