OK, I set core to debug and get this in the log when I press the button.
2019-03-03 07:37:35 DEBUG (MainThread) [homeassistant.components.websocket_api.http.connection.140015825214432] Sending {'id': 11, 'type': 'event', 'event': {'event_type': 'state_changed', 'data': {'entity_id': 'zha.zha_lumi_lumi_sensor_switch_aq2_02133f78', 'old_state': <state zha.zha_lumi_lumi_sensor_switch_aq2_02133f78=online; nwk=0x569e, ieee=00:15:8d:00:02:13:3f:78, lqi=254, rssi=-72, battery_size=CR2032, battery_quantity=1, battery_level=100, friendly_name=Office Lamp Button Online @ 2019-03-01T07:14:19.846953-05:00>, 'new_state': <state zha.zha_lumi_lumi_sensor_switch_aq2_02133f78=online; nwk=0x569e, ieee=00:15:8d:00:02:13:3f:78, lqi=254, rssi=-65, battery_size=CR2032, battery_quantity=1, battery_level=100, friendly_name=Office Lamp Button Online @ 2019-03-01T07:14:19.846953-05:00>}, 'origin': 'LOCAL', 'time_fired': datetime.datetime(2019, 3, 3, 12, 37, 35, 23802, tzinfo=<UTC>), 'context': {'id': 'c450c1cf3edf4537ada902cfdb43383e', 'user_id': None}}}
2019-03-03 07:37:35 DEBUG (MainThread) [homeassistant.components.websocket_api.http.connection.140015826874152] Sending {'id': 2, 'type': 'event', 'event': {'event_type': 'state_changed', 'data': {'entity_id': 'zha.zha_lumi_lumi_sensor_switch_aq2_02133f78', 'old_state': <state zha.zha_lumi_lumi_sensor_switch_aq2_02133f78=online; nwk=0x569e, ieee=00:15:8d:00:02:13:3f:78, lqi=254, rssi=-72, battery_size=CR2032, battery_quantity=1, battery_level=100, friendly_name=Office Lamp Button Online @ 2019-03-01T07:14:19.846953-05:00>, 'new_state': <state zha.zha_lumi_lumi_sensor_switch_aq2_02133f78=online; nwk=0x569e, ieee=00:15:8d:00:02:13:3f:78, lqi=254, rssi=-65, battery_size=CR2032, battery_quantity=1, battery_level=100, friendly_name=Office Lamp Button Online @ 2019-03-01T07:14:19.846953-05:00>}, 'origin': 'LOCAL', 'time_fired': datetime.datetime(2019, 3, 3, 12, 37, 35, 23802, tzinfo=<UTC>), 'context': {'id': 'c450c1cf3edf4537ada902cfdb43383e', 'user_id': None}}}
Also, no zha_event entries in the new event listener when I press the button.
Also, a binary_sensor entity was not created for this switch when I paired it which I find a bit odd as it is not consistent with the Xiaomi door sensor which does create this and does work. The problem I have with the door sensor is that it works for about a day and then shows as unavailable. I know that this is a different problem.