Gar
The PIK - BOH route is operated by a PIK based a/c however I do remember noticing on Tue that around 10 in the morning they already had a delay on the departure to BOH from 1400ish to around 1730 which seemed a bit odd. The flight was operated by a non based a/c which operates the FR415 from STN and instead of going back to STN at around 1730 as the FR422 it operated the BOH rotation and then (I think) operated the delayed 422 also some 3.5 hours late.
Pretty sure the a/c was EI-CSZ the one with the "Arrivederci Alitalia" titles.
Not sure of the "operational reason" but it was something they new about well in advance and put a plan of sorts into action rather than cancel the flight.
The An22 took some "stuff" out to Gostomel/Kiev in the Ukraine the following day so it was nothing to do with Ryanair.