Sensors FAQ
From nemeuswiki
Sensors stuck on SF12 datarate since the join procedure
The first data transmitted is always with SF12. This is to be compatible with most network architectures. For example, you can perform a join in SF10 but there is no guarantee that you will be able to communicate with the same SF.
The Network Server should use Adaptive Data Rate (ADR) mechanism to lower the SF.
If the device is stuck in SF12 despite good radio conditions (for example, in line of sight) it means that the Network Server does not manage ADR.