Factual error: When Martine enters the passcode to reveal the bats, you see her hit "3" first followed by what seems to be "5" (the rest is blocked by her body). She then tells Michael his passcode is the first 6 digits of pi backwards. The first 6 digits backwards would be "951413."
Factual error: During the ship scene, the computer graphic of splicing bat DNA into human DNA is wrong. DNA strands are complementary to each other. If you remove a segment from one side, what you can put back is predetermined by the other side, regardless of the source (bat, elephant, fish, etc). The graphic should have shown both sides of human DNA replaced (or just added) by both sides of bat DNA. As it is in the movie, the injection should not have any anatomic/physiologic effect.
Suggested correction: If you look it's been clear that Strange's spell wasn't perfect. Eddie being brought into the MCU when he had no idea who Spider-man was...nor did he die. Electro's new-look and having no idea who Spider-man was. If anything Clea, in MOM basically said he messed up. So that last spell didn't fix things. It's clear this is what they are building towards. Nothing is fixed. Either way it isn't a plot hole for this movie. Post credit scenes are usually teases for other movies to explain.