Major exceptions are typically things like null pointer exceptions that are not handled. Unfortunately, you really need the logs to begin to investigate what happened. It could be something with how the data restrictions are built out (site access, data restrictions on their security groups, conditions on the statuses, etc.), missing data on their record (such as not having a default insert site and something depending on that), different flows in automation scripts, etc. If it's data restriction related and the restriction is invalid in some capacity (references a column that doesn't exist for example), you likely would see the query in the logs. But if not, you should hopefully get a stacktrace of the error to help narrow down where the problematic code area of code is.