when the children are secured in a locked room on the alien flagship all of the children were seen being locked in the room, slo-mo made a dramatic entrance then part way through the sequence Slo-mo disappears and is not seen again until the children escapes from the chamber.
When the kids steal the alien space ship and just before Slo Mo is grabbed by Noodles, A Capella's mouth does not match the vocals she is supposed to be singing.