We have a Main line that rings on 4 phones at the same time for incoming calls. Those 4 phones also have their own individual line. When one of us is going to be out we forward our phone to one of the other 3 people. We just realized when any of us forward their individual phone, and a call comes in on the main line, no one else’s phone rings just flashes once and a missed call(s) message pops up, giving us no chance to answer. Tried search for this issue no luck. Not sure where to begin.