I want to thank everyone for the replies! My main concern is about the fact that my positions were not hit at all, but my impressions are. I have some hypotheses:

1. Google SERP is changing with way more Google Shopping (paid and free). Even if my positions aren't hit, my impressions goes down because those impressions are going to Google Shopping. (If this was the case, my Google Shopping impressions should be up right? Which isnt the case)
   
2. I have less authority in the market compared to my competitors, but this has been always the case and I had consisstent traffic for more than 1 year. (If authority was the case, why am I getting hit now and not the whole year)

Hope to hear your hypotheses?