I have noticed a few bugs on the GWE, within Scenearios, from what I can tell these only happen there, and not on 24 Hour Timetable mode. First bug is when trains facing towards Reading appear to have their lights facing the wrong way, (Red Lights for when it approaches, White Lights for when it's going away from you), this happens on both the Class 43 HST, and the Class 166, I can't say for sure if this happens on every single Sceneario, but the only sceneario where I know it occurs is on the "Down The Line" Sceneario. The Second bug is for the HST only (again this only happens in the Scenearios) Second bug is when the HST is seen from a distance, or when it's in motion, I noticed that the Coupler Bar appears when the Hatch is closed, it's only when it gets closer to you that it just disappears, i'm not sure to say wether it's inconsistent or not, but this is what I have noticed when I play a sceneario on the GWE. I will add more images if needed
Forgot to mention that the Sceneario for the 43 with the Coupler Bar appearance was "Christmas Closures"