A user on the forums reported an issue with their 7.3.0 nodes hitting java.lang.OutOfMemoryError: Direct buffer memory frequently. The nodes were being run with -XX:MaxDirectMemorySize=536870912 despite a 6GB heap. It turned out the heap size was being set twice:

-XX:MaxDirectMemorySize=536870912 would be consistent with JvmErgonomics incorrectly picking up that the heap is 1GB rather than 6GB. I don't have a way to reproduce this to investigate further but this feels like a bug somewhere along the way.