The new launch.sh script in EAP 8.1 for systemd incorrectly overrides JAVA_OPTS:

# Disable color output for the standard output
export JAVA_OPTS="${JAVA_OPTS} -Dorg.jboss.logmanager.nocolor=true"

If JAVA_OPTS is set before starting EAP, then EAP will not override it in standalone.conf and it must contain all of the default settings (such as -Xmx).
But launch.sh is overriding it, without setting the defaults.