Same issue here - I noticed today that “Goodbye” executed successfully, but after both my iPhone and Arrival Sensor were detected “I’m Back” failed to run:
2017-12-06 1:31:08.413 PM GMT APP system Status off Security system is set to Disarmed
2017-12-06 1:31:07.767 PM GMT DEVICE alarm off Siren event: off
2017-12-06 1:31:07.763 PM GMT DEVICE switch off Siren switch is off
2017-12-06 1:31:07.261 PM GMT LOCATION API piston Security Alarm Delay Sensor Basic piston executed in 92ms
2017-12-06 1:31:07.156 PM GMT DEVICE contact open Security Contact Trigger contact is open
2017-12-06 1:31:07.137 PM GMT APP_COMMAND open Security Alarm Delay Sensor sent open command to Security Contact Trigger
2017-12-06 1:30:53.545 PM GMT APP triggered true Alert with Lights has been triggered
2017-12-06 1:30:52.551 PM GMT APP triggered true Alert with Sirens has been triggered
2017-12-06 1:30:52.534 PM GMT APP intrusion alarm Upstairs Motion Zone intrusion detected.
2017-12-06 1:30:52.346 PM GMT DEVICE motion active Upstairs Motion Zone motion is active
2017-12-06 1:30:40.390 PM GMT LOCATION API piston Security Alarm Delay Sensor Basic piston executed in 82ms
2017-12-06 1:30:39.749 PM GMT DEVICE contact closed Front Door was closed
2017-12-06 1:30:36.589 PM GMT LOCATION API piston Security Alarm Delay Sensor Basic piston executed in 105ms
2017-12-06 1:30:35.925 PM GMT DEVICE contact open Front Door was opened
2017-12-06 1:30:30.811 PM GMT DEVICE presence present Guy’s Arrival Sensor presence is present
2017-12-06 1:28:34.333 PM GMT LOCATION API routine Home Fragrance was executed
2017-12-06 1:28:34.253 PM GMT DEVICE presence present Guy’s iPhone has arrived