UNIQUE constraint failed: nie:DataObject.nie:url
The source of those errors is identified: The
Resource table gets an element "garbage collected", even though the element still has data in other tables. Notably
nie:DataObject, in its UNIQUE
So the element "doesn't exist" to Tracker because the
Resource table is central to its workings, but the
nie:DataObject table still has the URI, so it won't be inserted twice. This results in the element failing consistently with the error in $subject.
Given the only paths that actually delete from the
Resource table are the resource garbage collection ones, there's some good chances the error is triggered through the triggers that perform reference counting on them.