ATSlave StackV1.1.0: Issue with network join status command after sleep

I am working with BL072z LoRa discovery kit which has ATSlave LoraWAN stack V1.1.0 flashed on it.

AT commands are send over LPUART from host controller

Gateway is used to connect to TheThingsNetwork

I am using AT+JOIN command to join the network and send data and go to sleep on host controller.

The power to discovery kit is always ON

After, I wakeup from sleep I re-configure the LPUART and send AT+NJS=? to check if network is still joined.

This returns status 0 meaning no network joined. Then I again send AT+JOIN and check network status using AT+NJS=? which shows it a success.

I am not able to understand as to why do I have to send the join request again after wake-up?

TheThingsNetwork shows that device is always connected.