Especially if the Blast was left in the racquet too long. RPM has an approx life span of 4 -8hrs of play depending on the players level. The stronger the player the shorter the life span. Check the tension in the racquet and I can guarantee that the string have lost 16-20lbs from the original ref tension. Poly strings do not have a ery long life span in general, but they are good at what they were designed for.
Yonex VCore98D;Tecnifibre RazorCode @ 44/40lbs
USTA,USPTA,USRSA*MRT,IART,TIA :Tennis begins with Love