Hi there - Lindsey here.
I can certainly take a look further into this for you. I've taken a look at your change history as well as your revenue, traffic and epmv data and I can see that your epmv has had a fairly consistent trend over the past month or so, however, it does look like an ad rule or filter was added that disabled a number of placeholders on the site which is likely part of the decrease you are seeing. When these rules are added and placeholders are essentially disabled or prevented from showing, then less ad locations can be tested leading to a decrease in your overall epmv which I believe is a key aspect in what has happened here.
To remedy this, it may be best to review any ad restrictions or pages without revenue and see if ads can be re-added or reviewed should there be any technical issues (i.e. with any pages without revenue, for instance). If you need any assistance with this, let us know and we can absolutely help with this. :-)