Bambino Back to Back

I don't know if this is a specific Bambino issue or a it's a general thing, but looking to understand what causes changes in Back to Back pulls on a Bambino.

So I have picked up a new grinder, just a nice value Encore ESP, so this morning I was having a first go with the current beans.

So shot one on the recommended 15 grind setting was way to fast.

Brought it down some and had a second pull, tasted ok, not great but ok.

So had a third go for a making into a Cortado, same grind setting but noticeably faster pull to the same output.

I have had this before also when hand grinding so I am assuming it is a quirk of how the machine works, or all machines work so I am just trying to understand which element of the process it is, i.e. group is now really hot etc....

I don't pull back to back shots often but always learning.......