64 bit source address of Xiaomi's Aqara Zigbee sensors changed to FF FF FF FF FF FF FF FF

I have one coordinator, router and few xioami zigbee sensor devices.The Aqara sensor’s parent is router and data is received at the coordinator via this router. Initially 64 bit source address in the data received from the sensor was
00 15 8D 00 02 B8 4D AA

But after turning power Off and On of coordinator, the 64 bit source address in the data received changed to

FF FF FF FF FF FF FF FF

Zigbee Sensor Data before power off was as follows.

Explicit RX Indicator (API 1)

7E 00 19 91 00 15 8D 00 02 B8 4D AA BF 50 01 01 00 06 01 04 00 18 10 0A 00 00 10 00 BD

Start delimiter: 7E
Length: 00 19 (25)
Frame type: 91 (Explicit RX Indicator)
64-bit source address: 00 15 8D 00 02 B8 4D AA
16-bit source address: BF 50
Source endpoint: 01
Destination endpoint: 01
Cluster ID: 00 06
Profile ID: 01 04
Receive options: 00
RF data: 18 10 0A 00 00 10 00
Checksum: BD 

After Power Off and On at coordinator

Explicit RX Indicator (API 1)

  7E 00 19 91 FF FF FF FF FF FF FF FF BF 50 01 01 00 06 01 04 00 18 16 0A 00 00 10 00 12
        Start delimiter: 7E
        Length: 00 19 (25)
        Frame type: 91 (Explicit RX Indicator)
        64-bit source address: FF FF FF FF FF FF FF FF
        16-bit source : BF 50
        Source endpoint: 01
        Destination endpoint: 01
        Cluster ID: 00 06
        Profile ID: 01 04
        Receive options: 00
        RF data: 18 16 0A 00 00 10 00
        Checksum: 12

Why 64 bit source address changed?