Hey,
I had the same problem after switching to FP Open and I have it again after upgrading to 16.08.0
although, the problem didn’t occur after the upgrade but only after re-installing google play services light through openGAPPS pico the problem seemed to be something with the native email client, the only work around I found was to deactivate the native email client and install the Gmail app from google play (or use K-9 mail) and use that instead. not ideal but the battery does last longer.
Anyone have any ideas how to fix this without deactivating the native email app?
thanks,