Here is observation from a poster on trackitt.com:
Posted by Burkino (92) 06 Aug 2007 4:19pm PST
The facts that we know:
1. Only 140 and AP (either approved or pending) got massive LUDs while 485 and EAD did not.
2. Only TSC cases got massive LUDs and not NSC.
3. There is a pattern of when massive weekend LUDs occured depending on the receipt number:
07/07 - SRC03...
07/14 - SRC04...
07/22 - SRC05...
07/28 - SRC06...
08/05 - SRC07...
My theory is that TSC run out of physical space to hold a few years worth of new applications to be received in a month until August 17. They decided to move 140/AP files to free up some space. They might moved them to different shelves, different rooms, different local storage facility or, for approved cases, even to the cave (a long-term USCIS storage in the abandoned mine in Missouri). Such relocations generated massive 140/AP LUDs across the board. Such relocations could indeed happened on weekends by junior/contractor staff in order not to disturb the work of adjudicators on workdays.
This is only a guess. But because we are all in a guessing game about these LUDs, this guess is as good as any other.