Neo4j-admin copy inconsistent behaviour

Dear Community. I am wondering if someone can help explain this behaviour.

(4.2.5, desjtop)

I have a database - profileid0 - which I want to copy to profileid361.

I am using the following command: neo4j-admin copy --from-database profileid0 --to-database profileid361

What I have noticed is that sometimes it is pretty efficient, but not always. This post was prompted by what I am experiencing right now. I ran this copy command - and noticed that it would take 4+ minutes to copy each 5% section. I shut everything down, restarted, and now the exact same command on the same DB is taking around 37 - 40s per 5%.

I don't know how to understand the root cause of this issue. My DB (profile 0) has
6m nodes
20m properties
9.7m relationships

my question is: how would someone who is much more experienced with Neo4j go about understanding and diagnosing this issue.