Account level reserve starting again?

Hi, for the past 6months or so Amazon stopped taking an account level reserve. All of a sudden they have started again and kept back all of my payment due yesterday. Can anyone help me understand why this might happen please? I am so confused. I don't know why they stopped last year, nor why they have started again now, it seems random and I would really appreciate amazon at least explaining to me why they are not paying me from one month to the next. Difficult to manage my finances as I never know if they are going to pay me or not. Very frustrating.

Thanks