The acid is wasted after being used, no matter what it hits.

If we break a vial of acid, its content is used and gone, no matter where it lands. It makes sense that acid conjured from a different place or straight out created from nothingness behaves the same way, even if it doesn't get to damage anything.

The energy resistance caused by those spells (all of them) does not stop the acid arrow spell from trying to deal damage every consequent round. Should the protection effects end or otherwise be discharged, the now unprotected target will still take the ongoing damage coming from the spell.