Could be a result of one or all of the below listed:

-Inferior serving material.
-Diameter of serving too great for your nock fit (too tight) causing rapid wear…and it will.
-Faulty installation of serving. Serving wrapped too loose....did not compensate for string stretch/creep.
-Etc.

I recommend using Spectra "Halo" or "No. 62 Braided Spectra-polyester blend" of a diameter best for your nock fit. Ever since I have used the "Halo," I do not have any problems with the serving breaking or unraveling. Then too, I use a "string loop." A "string loop" does wonders for reducing the wear and tear on serving.