Ring contact sensor is detected properly but doesn't trigger the alarm?

Hello all, my first time seeking support for a Ring issue that is befuddling me. Our alarm system seems to be properly set up on our wifi – all sensors are detected, and update in real time when doors are open or closed. In addition, our base station can fire off the alarm properly and does trigger when our front door is opened while the system is armed.

However, our back door does not trigger the alarm when it is armed. The alarm can be armed in Home mode, and I will go and open the back door, and looking at the app it will say “Back door - opened” – but the base station doesn’t indicate a problem.

I’ve searched all over for a description of this issue and can’t find anything. Has anyone encountered it?