Grafts started falling after 11 days post FUE surgery is it common?

In general transplanted hairs fall out within a few weeks after surgery. If you are concerned follow up with your doctor.

No need to worry, shedding of the transplanted hair can be noticed as early as the first week and can continue on to the sixth week. 

There is a possibility - due to operation stress - that a number of hairs will fall out in the post-operation phase. This generally temporary occurrence is known as "shock loss", and may last just a few weeks or possibly months. In certain cases, donor hairs and neighbouring hairs may fall out after a hair transplant (for instance when dense packing has been performed). This should not worry patients, as the hairs generally regrow once the shock loss period has ended. Moreover, the cell responsible for regrowth remains in the scalp even though grafted hair fall.

Grafts are usually shed between 1-4 weeks after receiving a hair transplant from the recipient area. Don't worry, its normal