This service is guard operated, when setting up your train at the start of the scenario remember to press Ctrl+Shift+R to enable guard operated doors. Please also remember that the maximum allowed speed of your Class 321 EMU is 100mph.
I have seen instances on different forums where this route has crashed for some people in the Stratford area. When 32-bit was the only option, I used to turn water quality down and this eliminated crashes or me. Since the addition of 64-bit, I haven't seen any crashes at all but that workaround could be an option for those that experience it.
Wherry Lines is one of the requirements for the Great Eastern Main Line route on the Steam Workshop. In order to see any of the Class 37 consists in this scenario, this requires you to own the Steam version of Wherry Lines. If you bought the route direct from Armstrong Powerhouse, the scenario will not be affected due to them being static consists.