(1) Please check the battery level. Make sure the battery level is not lower than 5%.
(2) If SMS2 is under BLE5.0 connection, the range is limited to BLE range only. So if BLE connection is poor, please consider setting up a Thread network for SMS2 for better connection.
(3) If the connection of SMS2 and the Thread network is too weak, try putting a Thread router to improve the Thread connection.