Flybe have one aircraft which nightstops at LCY - it operates the first LCY-EDI of the day and the last back.
From what I recall, the schedules which appeared briefly in the booking engine were an evening lcy-nqy-lcy, so it would be my guess that flyBe were tinkering with the idea of dropping out the evening EDI flight during the peak summer and inserting NQY instead.
This is quite common practice at lcy where demand for business routes drops right off during the high peak summer - BA Cityflyer, for example, already switch frequencies quite extensively from business routes onto the French/Spanish/Greek leisure routings during this period.