When Jim brings Kara to her room after the lake party it is late night however shots in her bedroom show daylight outside. The following scene when Jim an his friends leave the house, it is dark outside again.
The beer bottle Stiffler puts next to the cooler goes from upward, to lying down, to upward again.
The reunion in the school gym is held at night however when Jim and Michelle go to the music classroom to have their tryst sunlight is clearly seen through the large windows.
The rear view mirror has been removed from Kara's Mini Cooper.
On the way to Jim's old house, as the car drives past you can see Michelle wearing sunglasses for a split second, during the conversation about "the incident" they are nowhere to be seen. Later when Michelle steps out the car to hug Jim's dad, they appear on her face again.
[16:10]When all the guys meet in the bar, Selena shows them the YouTube video from 1999 with Jim dancing for Nadia on her smart phone. This isn't the actual video from Jim's web-cam, which is in the corner of the room. She used footage from the first American Pie movie itself, which is not possible.
At around 34 minutes into the movie Oz and Heather claim, both of them never had sex in public. Actually they had, as the fans know from the first movie. The first time they had sex was on the pier.
Finch tells Selena he "doesn't consider" French Guiana a country. It's irrelevant for Finch to say that because French Guiana in actuality is not a nation. It is an overseas department and region of France.