Southeastern Highspeed Mastery Rewards

Where is the mastery reward for southeastern highspeed (cargoship) meant to be.

 

I can't find it either... I assume it's meant to be around Rochester. I've got it clicked to show up in Mastery, but whilst all the requirements have been met, the level2 mastery till shows as locked?

 

Near stone crossing if you move your camera out to sea from the station

 

Can also be glimpsed from HS1 just before entering Tunnel 3 (Thames) in down direction... this can be a difficult view though.