Getting this?

Conflicting collector combinations in option list; please refer to the release notes for the combinations allowed

It could be because of this parameter in conjunction with the rest of the GC options specified.

ExecStart=/usr/bin/java -Xmx4096M -Xms2048M -XX:+UseG1GC -XX:MaxGCPauseMillis=200 -XX:+AlwaysPreTouch -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:+CMSIncrementalPacing -XX:ParallelGCThreads=4 -XX:+AggressiveOpts nogui -XX:+UnlockExperimentalVMOptions -XX:ActiveProcessorCount=4 -jar server.jar

But that wasn't the only thing.  It was also this option:

-XX:+UseParNewGC

Turns out that:

-XX:+UseG1GC

is a newer option that may conflict with the rest of the options as well. 

Thx,