ActiveMQ master node fail-over in 3 nodes due to unknowned reason

[梁坤红]

Hello!
I have a ActiveMQ cluster with 3 nodes. Version are Apache ActiveMQ 5.15.9. 
The master node failover 3 nodes due to unknowned reason. I attached the 
activemq.log here.
Please help me to check the reason. your support is highly appreciated.
Waiting for your reponse sincerely!