Hi Peter, I am no expert but i see the many occurrences of the following warning before your frontend server was given a shutdown command.
2018-06-22 02:39:04 UTC WARNING [WatchDog] Exceptionally high leap in time detected. During two executions of the WatchDog the time changed by 31214552 milliseconds. No time-outs of monitored threads can be noticed during this execution of the WatchDog. Potential root causes: Suspension of process / operating system during power save mode; WatchDog was not executed on time due to overcommited CPU If this warning should occur frequently, please check the CPU utilization and power-safing settings of your server environment. [log message will be suppressed for 15 minutes]
2018-06-22 09:01:14 UTC INFO [ShutdownPipe] got shutdown command on named pipe
2018-06-22 09:01:15 UTC INFO [FrontendServer] Shutting down frontend server. ShutdownType: SHUTDOWN
It talks about some over committed CPU. I am guessing you have some resource related issue. I would recommend you check the resources allocated to your server and open a support ticket with Dynatrace they should be able to suggest a remediation for this issue you are facing.
Hope this helps !!