Well, if I am not mistaken this happens after an agent just finished a call and is ready to receive another one, right?
If this is the case, then this is determined by the IR option which specifies the time after a call is routed to an agent before the next call can be routed to it. If I am not mistaken, it is usually 15 seconds.
The option you want to look into is transition ime. In a manual it says the following about this option:
Specifies the time, in seconds, that must elapse after an agent that had received an interaction from IR was
reported as ready before IR starts routing interactions to the agent again. A positive value is useful when it is possible
for an agent to pass through ready state in a transition between ending an interaction and making himself
unavailable by a manual command.
Well, hopefully, it will fix your problem. but if you really think about it it is not really a problem at all. Of course, if this is not the reason for a blocked DN, then let us know again.