Yes most cars have some form or over reporting but its usually in low single digit percentages but the Leaf Always is 10% more.. ( by design it seems )
The VW Golf I drove recently (2018 model) and the Leaf both underreported speed by 5km/h judging by the 'your speed' sign on the side of the road.
How are you judging the actual speed vs the speedometer?
Its been mentioned on a number of overseas forums and I have used multiple GPS devices in multiple Leaf's and its pretty much 10%
just google "leaf speedo 10 percent"
TBH I think it is conscious on the designers part to maximise the real world range of the car by minimising the actual speed being driven...while staying within the regulations. In theory that would apply to ICE cars too but the range of an ICE car isn't normally its limiting factor in most people's minds...just my $0.02