The tent that Judy and her boyfriend are camping in changes size between shots.
The video monitor and VCR on Dr. Crews' desk disappear as Tina looks at the picture of her father.
(at around 1h 13 mins) As Jason steps out of the puddle, his clothing is dripping wet. Then in the next shot, as he walks after Tina, his clothes can be seen as dry.
In Friday the 13th Part VI, the sheriff shoots Jason in the head through the mask, leaving a hole in the top of it from the bullet. In this film, the hole in the mask is gone, although the boat propeller damage still there from Part VI (the hole in the head of the mask) is not when it should be.
(at around 21 mins) When Eddie is reading stuff from his pile of paper, the pile is disordered. When the camera cuts to the pile, it is neatly stacked.
When Melissa comes into the kitchen asking where Nick is, Robin says "I think he went next door to visit Marilyn Munster." This couldn't possibly be an insulting nickname, as Marilyn Munster was the only normal one in the Munster family.
(at around 1h 16 mins) After Jason pulls the axe out of the tree stump, there is no cut mark left in the stump where the axe was previously stuck.
(at around 1h 1 min) Cameraman's shadow on the wall just before Robin knocks on a door and says "Maddy"?
(at around 1h 3 mins) Reflection of crewman holding boom mic in the window that Robin passes by when she's alone in one of the bedrooms.
(at around 52 mins) Cameraman's shadow on the side of the van when Ben is looking for Michael.
(at around 51 mins) Lighting equipment is reflected on the side of the van as Jason spies on Kate and Ben.
When Tina finds her mother's body in the woods, there's a close-up of Mrs. Shepard's face. At that moment, you can see someone's foot enter the frame at the top-left. It's either a crew member, or Jason was supposed to enter the scene.
Jason is a corpse yet he can be seen breathing quite heavily in some scenes.