N707ZS
Neither JOTA nor SEN have commented on that subject as far as I know.
There have been rumours of JOTA being less than happy with aspects such as reluctance to grant them night slots and the requirement to despatch all their departures from terminal stands, be they revenue or simply positioning flights. I doubt that the reasons for the move will ever appear in the public domain but it looks to me that SEN didn't try very hard to retain their business.