Draft terms of reference for the inquiry have appeared at
Terms of reference | Regulatory Policy | About the CAA
It mentions
including the measures that had been put in place to prepare for routine changes to systems that had occurred on the 11 December 2014 date for the regulated changes to aeronautical information (the AIRAC date) and for the move of additional workstations to support the military task that was re-locating from Prestwick.
and
- The preparation and testing of premeditated operational/engineering changes to systems and procedures planned to take place on or about regular AIRAC dates or in association with particular infrastructure changes.
which is the first time I have seen links to system changes as being a potential contributory cause.