Antminer S9 13.5Th/s is giving 9.5Th/s only I just bought a new antminer S9 model 13.5Th/s. 

The problem that the average hash rate doesn't exceed the 10Th/s as attached in the picture, anyone knows why? 

Thank you in advance.
First of all - check your logs on the miner and then the status via the buildt in GUI on the 9S.

From what i can guess, one of your hashboards arent running. 
And there can be several reasons for this.

Reboot the miner,
Update Firmware,
Check PSU,
Check Netcable,
and Check Fans

IF non of this helped you need to look into the logs more closely,.
a board might be defective.