Especially 12 strand B50. Less so with 16strand B-50. Even less so with 8125, and even less so with 450plus. Surprised your shooting 12 strands with a 55lb bow. I would probably shoot at least 16.

Another thing to look for is if your string is twisted quite a bit to adjust for stretch or you had a tad too long string to begin with and to adjust your BH, you had to twist alot, is the string will appear to be stretching during shooting more, especially if you unbrace the bow after shooting every time.