Who knows.. might have something to do with the train movement or something?
I know for 1 that, that changing the 'state' of train? if what i am getting it correctly, will allow you to perform actions without getting caught.
Think of it as 'Calm, moderately bumpy, extremely shaky'.
So far with the new update.
Some of the partners have a 'change train state' which lets you attack the target without getting caught. The harder ladies will capture you way too often due to the state of the train being 'easy-going', limiting the number of haressments you can do.
Changing the state permits those actions though there is still a chance to get caught.
There is the surround / siege state, which lets you unlock some CG scenes rather than animations. Grope - Fellatio - Outside CG scenes. Sadly, getting this CG scene means you be out of the train. Also, to get the surround state, you need 3-4 of your members around the yellow boxes of the target.
Only available for the top 3 girls. Pink-haired schoolgirl, Blue-haired MILF and Red-haired school girl.
If you want to unlock their animations, do not go into surround state. Though it also means you have chances of being caught. Fast Penetration (3rd Penetration animation) can be unlocked for the first 3 targets.
Sadly, the other 6 are still stuck at 2nd Penetration > Outside CG. Unless there is actually a way to get it.
Top 3 girls also have 5th and 6th scenes. Though it's just 1 with and without clothes. Unsure how to unlock them.
PS: Red-haired schoolgirl's siege 2nd Fellatio scene causes my game to black out. Could use some confirmation does it happen to anyone else.