How can I clear render cache or render memory

How can i clear render memory or render cache?
Maybe main reason is that my pc is short of spec.
but I have a trouble the follwoing.

Export mask channel is not correctly.
1th Render is almost correctly , but 2nd ,3rd is always different result
and mask result is incorrect. so I have to close D5 and restart for refresh.
but it is not good. if there is function of clear memory , I want to use it.

Sorry we do not have this feature yet, I will share this with our team.
Besides, could you share with me a screenshot of the mask channel issue? We will help you narrow down the issue cause first.

Thanks,
Oliver