We went to our sitemaps and discovered a fall in the number of indexed pages, while the submitted pages remained more or less the same.
Some sitemaps look like this now:
In the following sitemap the submitted pages went up, while the indexed pages has gone down:
And in some sitemaps the pages seem unaffected:
It could be a website problem where our pages are not accessible to Google. Could someone confirm that this isn't google playing around? Or that we aren't being penalised. This has never happened to us.
Also our search traffic has been actually going up for the past few months, so this is surprising.
This Question was posted on the 13th of May 2016.
This article came out on the 13th of May 2016: https://www.seroundtable.com/index-counts-in-google-sitemaps-reporting-drop-22078.html
Seems like there might be a Google Bug.