Yesterday Android OS on my Nexus 5 transferred 44,7 GB (!) data over both WiFi (42,2 GB) and mobile data (2,5 GB). I have no idea why the data transfer started, and I have no idea why it stopped after one day, and I have no idea what data was transferred, and to/from where.
I haven't changed or installed anything on the phone.
Is it possible to see exactly what data has been exchanged by the Android OS and why?