Basic scenario, Acid Cloud is casted ahead of a moving vehicle that has no time to avoid or slow down. So the vehicles own movement carries it into the cloud and the occupants/vehicle take damage.
Would this cancel out Invisibility? As the vehicle movement happened after the spell was casted?
I ruled that this wouldn't cancel out Invisibility as the RAW states " For purposes of this spell, an attack includes any spell targeting a foe or whose area or effect includes a foe. Exactly who is a foe depends on the invisible character's perceptions. Actions directed at unattended objects do not break the spell. Causing harm indirectly is not an attack. Thus, an invisible being can open doors, talk, eat, climb stairs, summon monsters and have them attack, cut the ropes holding a rope bridge while enemies are on the bridge, remotely trigger traps, open a portcullis to release attack dogs, and so forth. If the subject attacks directly, however, it immediately becomes visible along with all its gear. Spells such as bless that specifically affect allies but not foes are not attacks for this purpose, even when they include foes in their area."
Which I interpreted as since the cloud did the damage to the vehicle because it wasn't able to stop in time, that the Invisibility wouldn't be canceled out.
Hopefully that is clear enough for how the situation is.
Thanks for any input provided. :)