Ring not sounding alarm when the contact sensor is disturbed

I have installed a Ring Alarm System with 5 sensors on doors and windows and a motion detector. I have two questions: 1. When we come home with the Ring system set to "Away" and open a door, sometimes the alarm will start to ring immediately an some other times it will start a countdown and will ring unless you disarm it by entering the code. Why two different behaviors??? 2. (First point become mute when this started happening) For the last few days, I have seen that the alarm is not activated if I open a door with a contact sensor installed. I tried that with two doors and it doesn't work instantly. And earlier it used to work with all doors. Yesterday it worked but it started ringing about 3-4 mins after I opened the door. I would be thankful for any help, RJ