Fortnite just can't seem to get its shopping carts to work. After being disabled a few days ago due to bugs, they returned this morning only to be disabled again less than two hours later, again "due to ongoing issues." Those issues probably have something to do with a bug that can clip you through the map when you dismount a shopping cart. Sometimes this bug just kills you, but as this YouTube clip from A4 shows, some players have been using the bug to get cheap wins:
Falling through the world is a pretty serious issue, but it's also possible Epic simply wanted to delay yet another shopping cart tragedy.