SX70/SLR680 Film door swap. Fixing the "divot"
Do your impossible images have a small undeveloped patch at the top? Are you using a SLR680? If so, then you may want to try this to solve the problem. It eliminated about 95% of divots from my photos. Every camera is different, so this may or may not work for you, but it's worth a shot. You will need a film door from a SX70 camera.
Explanation: The SX70 rollers squeeze the developer (liquid chemicals used for development) more tightly and evenly than the SLR680 rollers. I'm not sure why they changed the design, but I do know that impossible film has a slightly different thickness than the Polaroid film which was originally intended to be used with these cameras.
Do so at your own risk. I'm not responsible for damage to your camera.
If you're having trouble viewing this video, it is also available on youtube.