Why this bias? (Process)

I had a new set of samples for validation (process system), as I said in other posts, this is an exciting moment: Will the  calibration performs well?

My first reaction is to look to the plots (Lab vs Predicted). In this case I had this surprising plot:

There are some samples marked as x which have a bias. These are 12 samples (one for batch of flour production), taken randomly during the batch production. It is clear that something happened during the process, and that produced a bias, giving 3 points more of protein during that period.

I expected to have the same problem for moisture, ..., it was not so much, but all these samples has also a bias , being the residuals (Lab - Predicted) positive for all of them.

Same for ash, again these samples are apart from the others.

It is clear that something is happening with these samples. We have to take a look to the spectra.

To be continued.....