Does the server restart directly after startup or is this a random shutdown and restart after running for some time.
Does it reach "Web Tier initialization is complete"?
Is there any Shutdown initiated entry, perhaps after cluster joining attempt failed for hazelcast.
There are reasons an instance will shutdown ... but I can't think of any that would cause it to restart itself. However, if you have a batch process that restarts a downed node, that would explain that piece.
My Pega 7.3.1 runs on the below WAS and IBM JVM and I don;t experience any issue:
WebSphere Platform 126.96.36.199 [ND 188.8.131.52 cf131801.05] [IBMJAVA71 184.108.40.206 cf131751.02] [IBMJAVA8 220.127.116.11 cf131751.02] running with process name wchans3w7Node28Cell\wchans3w7Node28\PEGA731_WAS85_SPLITSCHEMA_SERVER and process id 17220
Host Operating System is Windows 7, version 6.1
Java version = 1.8.0_151, Java Runtime Version = 18.104.22.168 - pwa6480sr5fp6-20171124_02(SR5 FP6), Java Compiler = j9jit29, Java VM name = IBM J9 VM