The peaks are on Saturdays so my guess is residential ISPs/personal traffic peaking on weekends while the mon-fri 9-5 are on older legacy IPv4 systems. But that's just a guess as the reason why.
Thanks, that makes sense.
Also, perhaps more people are out and about using mobile networks rather than WiFi on the weekends.
Office workers accessing the internet from their offices perhaps? My understanding is that NAT’s are more common for residential connections