Chunk start loop executes faster than the user interface reflects

I have an operation where I write records to the database within a loop, and recently I found that while my loop is still on the prefinal execution (I did a step loop execution), the final iteration already took place.

There is no other way that the data could have been processed and written to the database, so it really must have happened in the loop.

Is it possible that the chunk start loop is actually running iterations in parallel?