Hi
I'm using bacnet4j stack from 3 tears ago and not able to unsubscribe to COV although the PDU response for unsubscribe is success.
registration is for life time and the way I Subscribe and Unsubscribe is as follow:

Subscribe:

req = new SubscribeCOVRequest(new UnsignedInteger(1), aoid, new Boolean(true), new UnsignedInteger(0));
ocalDevice.send(d, req);

Unsubscribe:

localDevice.send(rd, new SubscribeCOVRequest(1, oid, null, null));

BTW:Is the process Id number should be same ?