I have a fuel station that's not strictly reachable by truck, being inside a loop of train track. However, trucks can get close enough to refuel, and the truck assigned to the station ran for a while without problems. At some point recently, it got stuck, unable (apparently) to get close enough to refuel but not raising any kind of alert.
Manually moving the truck can solve it, but doesn't always. The manual move shown in the screenshot didn't actually; the truck ended up stuck in the same spot. But another, similar manual move (just a bit farther to the left than the one shown) did resolve it.
Truck got stuck the same way after one trip, so here's the save I forgot to make before: