@junior_h Thanks, I've set these to 1G, as this is my expected heap size. Problem hasn't gone.
I came across this post: Memory confusion in Ubuntu 16.04
and realized that I don't need to lock the memory as I don't have swap on my node anyway.
Not sure if this might be reason for the memory_lock setting to not work, as it clearly says it's a RLIMIT_MEMLOCK issue.