Hi
In MEGACO there is SUB message which deletes a specific Context.These message could either be because of a normal or abnormal circumstance.Normal case is when a MS disconnect for MOC or MTC or when MSC-S receives a release message. in Abnormal situation due to some reasons like as Dual Seizure or congestion .. one context should be deleted (Usually TDM-TDM ,IP-TDM)
in this time even some context might be lost! so in my opinion the best way to see why a context is deleted or lost, is to find the related release message form BICC or ISUP interface.