GRPC io.grpc.StatusRuntimeException: UNAVAILABLE: io exception

The code model looks like as

 Iterator iterator = grpc.invokeSomeRequest(requestData) //returns iterator
 while(iterator.hasNext()){
     //do some code.
 }

Sometimes the error occurs at iterator.hasNext() with stack trace:

UNAVAILABLE: io exception               
io.grpc.StatusRuntimeException: UNAVAILABLE: io exception                                                                                                                                
     at io.grpc.Status.asRuntimeException(Status.java:533) 

A version of grpc is 1.21.0

I figured out that this problem most likely at grpc. I could be wrong. What is the best workaround for this problem?