Error messages occurs when a set of records is added to a set:
"Errors occurred when trying to access /index.php/batch/Editor/Edit/set_id/30:
Set is empty"
It has occurred in sets for various record types including entities and occurrences:
(Login: admin; password)
The issue is difficult to replicate because it happens intermittently. It tends to happen with large sets of records.
Also, sometimes the number of records that is shown in the "Your search found..." statement is not the same as number of records that shows in the batch edit form when "Open for batch editing" is checked.
See the screenshots. It says my search found 12,572 records. But the batch edit screen says editing 5792 occurrences in set. The 5792 number matches the number in the "History" dropdown in the first screenshot.