I have a boat that goes between an oil rig (Dreningbury Valley) & a dock, I also have a hover boat that goes between multiple oil rigs. For some reason both of these boats got stuck at a single rig (Dreningbury Valley). It's very bizarre:
I've tried changing their destination to the depot, changing their destination to another rig, skipping a destination, removing all destinations and starting over, creating a closer depot for them to go to, etc. None of these actions have helped. I was hoping that this rig would eventually disappear form lack of activity, but it still registers a ~20% transport rate for both oil and passengers, so I doubt it's going to go away.