shantui 245 excavator

good day currently working on a shantui 245 excavator the machine developed a problem where it cuts off under heavy load instantly. this problem has happened infield normal diagnostic procedures have been run. machine was brought to workshop and went through found nothing then machine then worked two days before cutting off 3 times it was loaded to a new site and worked a full day with no issues. today again it has suddenly cut off. any ideas or i formation would be greatly appreciated. kind regards