Graph QL throw error like complex query

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WebAPI2

We are using Graph QL in our application(Webapi2).
We wrote code for mutation and Query.
We using single controller for all Graph QL app.
But some time it's thrown error and service go down. On the time if call any service in Graph ql, it didn't work. Once we restart service , then only service get up. Other we can't make up.
Same query working fine in Dev environment.
I want know this is environment issue or not. How can i resolved?
Can anyone help for this.

Error generating like as below.

Message :Query is too complex to validate.
Code: INVALID_OPERATION
InnerException :Query is too complex to validate.

What I have tried:

i tried to reproduced in our local. But i didn't get any error. Error is occuring in live only.