Handle edge cases in backup

**Problem**
When working with data, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

The issue does not name a file, backup entry point, or test. Start by locating the backup implementation and reproducing its current error cases, then trace where errors are reported. Done means the relevant backup failures produce detailed, useful messages and coverage exists for the handled edge cases.

Written by the indexing model from the issue text.