ADB server crash constantly every 2hours

We are running appium to test an android APP and the test last for very long, like 24 hours.
But when the tests are being executed,we would encouter case that the under lying ADB server is crashed and need to be restarted. We have an loop in our server to periodically check connected devices and below are some logs that we observe from an overnight test execution, and the log shows every 2 hours and 5 mintues, the adb server would be killed.
Anybody know why?
Log snippets:

12-06 19:30:00.009 [scheduling-1] INFO c.wz.autobot.shell.AdbCommandRunner [40] – Using ADB to list connected devices

12-06 19:30:02.092 [pool-1-thread-5] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon not running; starting now at tcp:5037

12-06 19:30:02.141 [pool-1-thread-5] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon started successfully

12-06 19:30:02.156 [pool-1-thread-1] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT: List of devices attached

12-06 19:30:02.156 [pool-1-thread-1] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT:

12-06 21:35:00.011 [scheduling-1] INFO c.wz.autobot.shell.AdbCommandRunner [40] – Using ADB to list connected devices

12-06 21:35:02.106 [pool-1-thread-1] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon not running; starting now at tcp:5037

12-06 21:35:02.155 [pool-1-thread-1] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon started successfully

12-06 21:35:02.169 [pool-1-thread-5] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT: List of devices attached

12-06 21:35:02.169 [pool-1-thread-5] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT:

12-06 23:40:00.009 [scheduling-1] INFO c.wz.autobot.shell.AdbCommandRunner [40] – Using ADB to list connected devices

12-06 23:40:02.089 [pool-1-thread-5] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon not running; starting now at tcp:5037

12-06 23:40:02.140 [pool-1-thread-5] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon started successfully

12-06 23:40:02.142 [pool-1-thread-1] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT: List of devices attached

12-06 23:40:02.142 [pool-1-thread-1] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT:

12-07 01:45:00.001 [scheduling-1] INFO c.wz.autobot.shell.AdbCommandRunner [40] – Using ADB to list connected devices

12-07 01:45:02.126 [pool-1-thread-3] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon not running; starting now at tcp:5037

12-07 01:45:02.176 [pool-1-thread-3] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon started successfully

12-07 01:45:02.178 [pool-1-thread-1] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT: List of devices attached

12-07 01:45:02.178 [pool-1-thread-1] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT:

12-07 03:50:00.006 [scheduling-1] INFO c.wz.autobot.shell.AdbCommandRunner [40] – Using ADB to list connected devices

12-07 03:50:02.111 [pool-1-thread-2] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon not running; starting now at tcp:5037

12-07 03:50:02.160 [pool-1-thread-2] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon started successfully

12-07 03:50:02.176 [pool-1-thread-4] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT: List of devices attached

12-07 03:50:02.176 [pool-1-thread-4] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT:

12-07 05:55:00.002 [scheduling-1] INFO c.wz.autobot.shell.AdbCommandRunner [40] – Using ADB to list connected devices

12-07 05:55:02.107 [pool-1-thread-2] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon not running; starting now at tcp:5037

12-07 05:55:02.157 [pool-1-thread-2] INFO c.wz.autobot.shell.AdbCommandRunner [48] – ADB SHELL ERROR: * daemon started successfully

12-07 05:55:02.171 [pool-1-thread-5] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT: List of devices attached

12-07 05:55:02.171 [pool-1-thread-5] INFO c.wz.autobot.shell.AdbCommandRunner [45] – ADB SHELL OUTPUT: