The phrase "to lack some substance" means that something is lacking depth or significance. It suggests that there isn't enough substance or value in whatever is being referred to. Full definition
But that doesn't mean the film lacks substance when it's needed. (thecriticalcritics.com)
A specially formulated baby lotion will definitely lack any substances that might cause harm to the baby's skin. (thankyourbaby.com)
The story and environment are very interesting and enjoyable, though some of the characters lack substance and are easily forgettable. (metacritic.com)