The other callback to the original Incredibles comes in the form of super suits.
It turns out that protecting the left shoulder of a super suit must be hard work, as Elastigirl sees her new suit, as seen in the trailers, get torn in the exact same place.
Considering Elastigirl’s suit came from a different designer, it seems the issue doesn’t have anything to do with Edna’s design.
Superheroes traditionally have some sort of special weakness and while we’ve never had one specifically mentioned in the Incredibles movies, perhaps this is it.