This is a bit complex to explain, so I will do my best to simplify it. I have a network of websites on a host of popular topics which have been around since 5 years minimum, some are even older. They are actively updated - multiple times every working day with original content.
1) All the websites are hosted on a single server with a static IP.
2) I serve ads using two separate adsense accounts but they are not combined on one site. For eg - Site A will only show ads from account 1 and Site B from Account 2. (I understand Google does not advocate separate Adsense accounts for websites but I had to do this from an accounting point of view).
Things changed for the bad after the weekend -
1) Usually I receive a steady stream of visitors from Google. There are no spokes or dips only a fall during the weekends but that is also predictable. However starting Monday all the websites that were been served ads from one of my Google Adsense accounts dropped in serps consistently. All of them saw a drop of 50% in clicks and 70% in impressions.
2) The websites served by the second account remain stable.
Had it been for a single website I could have thought it to be normal, but all the website been served from a single Adsense account is what makes me wary.
What are the actions should I take now?
1) Write to Google for a re-inclusion in the index? Maybe the sites very sandboxed, highly unlikely but a rare possibility.
2) Get new IP addresses and split the websites across the addresses.