What's the heap and perm size configured for this instance? If you are running Jboss/wildfly with 32bit JDK, there is a process size limitation of 4gb.
My Wildfly are running for default, At the beginning it works well and little by little it fills until it causes the overflow
you have memory leak in your application somewhere, probably in one of the cron jobs.
best thing you can do is attach profiler and profile it.