I have a number complete TV series. And I obviously treat these as box sets.

And if and only if a complete series has yearly series that are sets, packaged separately,
(slip cases), and the slip cases have UPCs, I treat these slip case as box sets with child profiles for their discs.
I have tags for these multi-levels. The outer level is tagged level-1,
and thee inner yearly boxes sets are level-2.
The all discs of all box sets are tagged as child profiles.
I also have tags for the type of TV set, place of purchase, etc.

Some, but not all of my level 2 profiles disappeared and their children became un-boxed out side of level-1. I could not find any pattern in this disappearance, neither date of creation nor title. Not all the children were freed. In some the disappearance was total, but like in the instance of Walker, Texas Ranger: The Complete Series one level-2 remained intact.

Examples:
Dr. Quinn, Medicine Woman: The Complete Series has the yearly series packaged separately,
(slip cases), but these cases have no UPCs, so this set's inner slip cases are not profiled and treated as a level -2. I do use the their covers for the disc profiles.
where as....
Walker, Texas Ranger: The Complete Series has the yearly series packaged separately,
(slip cases), but these cases have UPCs, so this set's inner slip cases are profiled and treated as a level -2.

I don't know when this happened, with some 15,000 profiles it is rather difficult to determine if and when something goes wrong.

I have spent most of the last couple of weeks finding the errors and rebuilding these lost profiles.
Finding these errors is not difficult, just time consuming, just look for the errant and unsupervised children and build them a new home.

What is interesting is that if I could retrieve the missing profiles from the on-line db the tags I have for the level, TV series and place of purchase were intact. I don't know where the tags came from.
All I had to do was fix the purchase date and notes. And if their child profiles were free, they even automatically retrieved their children.