For the second sensor is it reporting any activity? Is it possible that the battery has ran out?
I do have a beta firmware that I have been testing but haven’t finished testing it fully. It addresses an issue where the sensor stops responding in certain scenarios. When this happens the motion active / inactive still works, but certain reports are not sent. The device also will still wake up if you triple press the button on the back. If you pull the battery and put it back in the issue is resolved for some time. You can test the firmware but you may want to make sure that the issue is similar to the one listed above.