missing rows after using performance.py

[James Heather]

I've had another go running the performance.py script to upsert 
100,000,000 rows into a Phoenix table, and again I've ended up with 
around 500 rows missing.

Can anyone explain this, or reproduce it?
It is rather concerning: I'm reluctant to use Phoenix if I'm not sure 
whether rows will be silently dropped.

James