When placed on a gantry carriage contraption 2 redstones contacts that touch each others will not send a redstone signal while moving resulting in the redstone contacts sending a second signal when the contraption stops even if they were never pulled apart.
The left contact is glued to the gantry carriage and the right one to the pulley contraption (nvm it's actually the redstone links that don't send signals when moved)

Not moving

Moving

If the issue changes, I.E. you discover its a different thing that causes you should probably change the title to reflect that and/or make that clear in your description.
Also, using "nvm" generally means that it doesn't matter anymore, if that is the case you could close this issue.

redstone on contraptions is not calculated at all, a contraption is not a full replicate of the actual world but merely an entity.
Edit: that means, links can't send a signal as they don't actually exist when on a contraption

So it's not a bug it's a feature right ?

yup