Learn Italian: Ci mancano questi bancali per la spedizione. - We are missing these pallets for the shipment.

This is because mancare is an inverse-valency verb, meaning it is structured exactly like piacere. The English subject ("We") becomes the Italian indirect object (ci, meaning "to us"), and the English object ("these pallets") becomes the Italian subject (questi bancali). Because the subject questi bancali is plural, the verb must be the plural mancano.

Could ci in this sentence mean "there" (as in, "There are missing pallets")?

While ci is often used as an adverb of place meaning "there" or "here", when paired with verbs of lack like mancare, it is almost always interpreted as the indirect object pronoun "to us". If you wanted to say "There are pallets missing over there", you would typically rely on context or use a specific adverb of place, such as Là mancano dei bancali.

If I wanted to say "We missed the shipment" (because we were too late), would I still use this structure?

No. When meaning "to lack" or "to miss someone emotionally", mancare uses this inverse structure. However, when you mean "to miss an opportunity, a target, or transport", it acts as a normal verb with a direct object. That said, for missing a scheduled transport or deadline, Italians strongly prefer the verb perdere (to lose): Abbiamo perso la spedizione.

What exactly is a bancale? Can I just use the English word "pallet"?