I have run across very few mistakes in maps. That said I have had some real dangerous ones in USGS maps. Mostly in old ones and typically it is clear that when they were made in the last century no one actually went a looked at the area, they just drew what they thought it looked like. I do submit the errors to USGS but they rarely update maps.
I have run across dozens if not hundreds of mistakes on maps in my lifetime, fortunately have been in situations that are life threatening.
I agree with the cautionary tale of not going into places like Death Valley relying simply on a rented cars GPS, but maps are no guarantee of accuracy. If anything the fact that GPS’s exist probably has helped make most maps more accurate as now there are millions of people daily using the data, and money to be made by making sure the data is accurate.
I have seen a huge improvement in map data in the last 10 years myself, because now they actually have folks walking and or driving the actual roads every few years validating the data that was on some survey map from 50 or 75 years ago is actually correct... often it was not. Paper streets, one ways, legal streets that are steps, etc etc... all of which 10 years ago would just show up as a road on a map but be incorrect or impassible by vehicle, and sometiems even by walking a paper street that never was finished which is now woods. etc etc.