If your bike age more than 8 years, most common problem came from the part which is the 'One way bearing' or in the manual book stated as 'Cage' and 'Clutch shoe housing boss'. You can get this part easily and make sure buy the original part, the cost should be not more than RM40/set. Careful because this part contain 3 tiny spring attached to white plastic housing. To change this part, you need to detach the whole Clutch System.
You might need to check Auto Clutch Housing. If there's a mark or lining inside the housing; friction lane - it's time to change it with the cost not more than RM150/set, best to replace Clutch Shoe or 'Auto Clutch' at the same time if you have extra budget.
Attached is the image of Auto Clutch System for your reference. Picture taken from Yamaha Manual T135S/SE, edited by Nkamri. Credit to Yamaha T135 website for this manual book.