Phone intermittently rining on "Ring All" Strategy

Hi there.

I have a few switches set up and I have noticed that all phones don’t ring all of the time on my sales Queue. The queue is set up as ring all and all extensions are set up identical.

One site is using “Eyebeam” softphone - on this site the call notification box is not always poping up when a call comes in - but clicking the pick up button on the softphone allows the call to be picked up.

On the other site I have Cisco phones and one of the phones rings only intermittently, but again picking up the phone connects the call.

As both switches are set up the same I suspect a switch set up problem, can anyone offer advice?