Other mistake: Near the end of the film when Jack-Jack is manifesting various abilities, his first display is of the human-torch-type of superpower. This would have burned away all of his clothing, yet (for obvious reasons) his diaper remains intact. This is particularly apparent as designer Edna Mode's costume for Jack-Jack was earlier shown as fire-resistant, but he was not dressed in his outfit during this scene. (01:44:15)
Suggested correction: This is definitely intentional, not an error. We see Jack-Jack use his fire powers without burning his diaper in Incredibles 2. Having fire powers without burning clothes is just a retcon.
Continuity mistake: In the scene with Dash and Elastigirl in the principal's office, Dash's shirt keeps changing between shots. First it has a strange "X"-shaped fold on it, then it changes to relatively smooth, then BACK to the "X", and so on.
Suggested correction: Dash was only bending over and in the next shot he is sitting straight so he unwrinkled his shirt without noticing.
