Allow certain workflow transitions in "issue A" only if all their sub-tasks have a value on custom fields "user" and "date".
Add theĀ Logical validator to the desired workflow transition.
Add the following expression:
count(filterByFieldValue(filterByFieldValue(subtasks(), %{00070}, !=, ""), %{00012}, !=, "")) = count(subtasks())
Logical validator
Logical condition
count()
filterByFieldValue()
subtasks()