Currently on SEHS Class 66 journey TSW3 at the moment and being spawned on foot at random stations when starting 6Y08. Have spawned once by a 66 but it wont let me take over the service without ending Journey event so currently just riding it towards hoo junction to see what happens.
Upon riding the train which was the correct service to hoo junction it triggered the objective markers and completed the scenario without me being able to drive it. I thought the spawn issues on SEHS had been resolved which is unfortunate. Journey mode was ticked off following this but obviously no points awarded during the drive over left a bronze medal too (but then scoring issues are known on the route).
Just found this thread after spawning on foot twice at different locations with no trains in sight. I found this was supposed to have been fixed by a patch last July, but I only downloaded the DLC since installing TSW4, so no. Edit: Ditto 6Y71.
The way to solve the spawn on foot issue in services is spawn on foot mode at departure station (Dartford for 6Y08 and 6Y71) few minutes before the train arrives and you're able to climb aboard and take service. I've solved this way these services and others in different routes