Just off the top of my head :
Incorrect map data - a road I take from my house to the nearest town keeps getting edited down, on one of the mapping sites that multiple car manufacturers use, to a 30mph limit when it is a NSL road (ie, nominally 60mph). I keep changing it back to the correct setting, but it gets reset within a month or so.
Errant speed limit signs - there is a lone 30mph sign on a side-road on the way home from the local town, which every modern 'sign-recognition equipped' car I've been in has read as the de-facto limit for the main road I'm on, which is a NSL road. The sign has been there for at least a decade but the council hasn't removed it despite multiple requests over the years (there is no 30mph limit on the entire stretch of road it stands at the head of). There is also a road that heads off from the main road, but is straight-ahead as you look at it, and this has prominent 40mph signs. Yep, all the cars pick that up and decide the NSL road is now a 40mph limit, overriding the map data that thinks it's a 30 or a 60, depending on which mapping data they are using. Both of these are within a mile of where I live.
A friend's '22-plate' VW keeps deciding that the motorway is a 100mph limit at random. It has been suggested, though not proven yet, that the camera sign recognition on the car is reading the speed stickers on the back of lorries and not realising that '100' on a foreign lorry isn't the speed limit.
GPS misidentifying your position and deciding you are driving in an adjacent industrial estate that has a 5mph limit, whilst you are in a 30mph limit
As with the other 'driver assistance' tools, like lane-keep assist et al, I'm sure that if you are driving predominantly on motorways or well-maintained wide carriageways, then the system probably works, but in the real world where signs have not been placed with this wonderful technological future in mind, it simply isn't fit for purpose. And good luck getting our bankrupt councils to worry about removing, replacing or changing orientation of all the road signs in the country.