sounds to me like the nock point has moved and is not set right when they re-served the string. If the pins are roughly in the same area, and the peep hasn't moved and your anchor is the same, then it probably has to do with the serving. Either the nock point height (which will effect both flight and your pin settings if it moved since it changes the distance to the peep) or the nock fit to the string is way off.

--Bob