All 4 sites are about 6-9 months old (e.g. I add one or two pages every week) so have about 40 pages. This rankings drop has occurred to all the pages. Every single one of them. So one of my sites which averages about 600 visitors per day now gets only a fraction of that.
The websites sit on the same hosting. Here is one of the sites accountingcertificateprograms.org.
I have gone back through my spreadsheets and actions and I don't beleive I have done anything really different for the sites over the past few weeks. My SEO has been consistent and I haven't done anything out of the ordinary from what I can tell.
Also, for 2 of the sites, off page SEO (e.g. majority backlinking) stopped about 3 months ago so there hasn't been any aggressive linkbuilding or anything like that.
I have 6 other sites that sit on that hosting and they were not impacted at all.
Can someone please offer some advice as I've been looking at this for hours on end now and have no idea what happened. I've never lost my rankings ever... I have only ever improved my rankings so this is a first for me.
Is this a penalty for something? Or maybe a manual review etc.
Any advice so I can make a start to investigate would be greatly appreciated.