Most recent experience, we were in the docks, the docks are restricted access for terrorism prevention, on entry you need a specific purpose. Our purpose was to inspect a possible party venue (an actual steamship, it's awesome, for a few grand we could have them steam it out into the sea while we celebrated - but, on viewing it seemed like if weather was bad on the day it'd suck as a venue because there's only very limited indoor capacity). So after we've looked around we need to get back out of the docks. Friend summons an Uber. No problem initially, "This is why I use Uber" she says. Her ride gets to the edge of the docks and cancels, presumably because the driver sees scary warning saying "Restricted Area. State your business at checkpoint" and hit cancel because he has managed to live in a port city for years without knowing about this. She summons another one. It too gets to the edge of the docks and then cancels. "Uber says if this keeps happening they're forbidden from cancelling" she claims. Sure enough now her requests are just denied automatically.
So once she gives up I called a regular taxi. That driver couldn't find us, because apparently a massive sign with the name of the ship is too hard to notice ("I had no idea that was here"), but once we walked a few minutes to somewhere this driver could recognise we were driven out of the docks to go for cocktails with another friend.