(at around 1h 45 mins) Scott's face has no blood on it while being heavily covered in blood in the previous scene.
It is highly unlikely that there would be an Earth-like perfectly breathable oxygen/nitrogen atmosphere in the Quantum Realm. Since the characters are existing at a scale smaller than the atoms which compose the gases humans breathe, one must suppose a suitable, breathable, replacement exists in the quantum-scale environment.
(at around 23 mins) Masseters (the jaw muscles) are the strongest muscles in the human body, so there is no possibility for someone to hold someone else's mouth open forcibly as it is happening when Ant-Man drinks the red liquid. However, the people holding his mouth open aren't humans, so are very likely to have above-human strength.
(at around 24 mins) Cassie has dried red liquid on her chin. Scott's face is void of all stains.
Veb is shown to reabsorb with ooze off of Scott's face, and later absorbs the ooze off of Cassie's face as well.
Veb is shown to reabsorb with ooze off of Scott's face, and later absorbs the ooze off of Cassie's face as well.
(at around 34 mins) Ant-Man's jaw does not match the utterance of "Van Dyme" when he tells Janet's name to the rebel leader.
(at around 8 mins) Janet Van Dyne talking to Hope about the quantum realm says she spent thirty years down there, when she returned she was thirty years older. In Avengers: Endgame (2019), Scott tells Natasha and Captain America he was gone five years and says it was like five hours, time is different in the quantum realm. So if what Scott says was true then Janet should have only aged thirty hours when she came back from the quantum realm.
(at around 42 mins) The laser-head character waits to be held by three laser ropes before deciding to free himself by killing his opponents with a simple rotation of his head.
(at around 38 mins) Janet supposedly is a fighter and a leader but she uses "uptalk" when telling/asking her husband to "cover me?!" before commandeering the ship.