well if the insulin is running down your chest then it wasnt an occlusion. if the pod is still giving insulin it's still working, it will sound the alarm if it is blocked, and not able to give you the insilin. If the cannula has fallen out of your skin, the pod doesn`t know that and is still sending insulin.
Also for your back try leaning slightly forward when you stick the pod on, I find this helps me. do not play with the tape once it is on or before you will make it Stick less. also maybe try using skin tac when you put it on your back to give it some extra adhesive.