Royal Enfield — Rear side Semitrailing arm's bolt broke up

Address:

411044

Hi, I am Shirish Kalbhor using electra 350 since last 5 years. On 18 Jan 2017, while going to office on speed breaker I heard loud sound of breaking something. later on i got to know my electra's rear side semitrailing arm's bolt broken up into two pieces. How could this bolt broke ? What would be the reasons behind this ?. I request you to replace this broken bolt into new one.