Has anyone run into a situation where the relation set between two cursors (both created using create cursor command) has been unreliable?

I have recently run into a situation where at a single customer code that has been working fine has been freezing. In tracking down the issue I have found that the logging indicates that the relation is being lost between two cursors. The problem is that the issue does not replicate, that being between one run and the next it does not replicate. However, the user has been getting the issue once or twice a night. But when running the process against the same data the issue cannot be replicated. It appears pretty random. The record at the point of failure for the second cursor is at end of file.