To dial into the port with no answer on Mitel doesn't means nothing. Did you go into Maintenance to take a look on the status of that port. Is it idle or busy out? Do not forget that last port is responsible for MW light ON & OFF. If this is busy Hottel take it out of Hunt Group in Form 17. Leave it alone to turn MWL.Because if calls comes into port 4 at the time what ever port doing its main job(MW)it would not Answer.
set up Hunt Group for Terminal not Circular hunting. In this case ring would come to first port in the group first and will hunt in order.