What does it mean if the string breaks at the sweet spot? That happened when I was using bg68ti, only one week old :/
I'd normally say that's general wear & tear, your hitting it very hard with a very high tension. Unless it's s string defect or your stringer caught the string on a sharp gromit of a clamp & the weak point of the string just ended up in the sweetspot area. Only way to rule that out is to inspect the newly strung racquet & check for a pinched string or fraying.