Rear Hatch Will Not Securely Close

Hmm, haven't had this issue with the Prius, but I have with other cars. Maybe start by making sure the latch area in the trunk sill is clean and unobstructed and the trunk mat, etc is clear from the sill. You could try some grease on the latch. See if having another door or window open makes it easier, to reduce the air pressure push-back.

The only quirks I've found with the hatch are with the struts--the seals get dry and static friction goes up (a little grease helps this too) and they don't provide as much force when the temperature's cold.

 

I had this exact problem after my wife carted a load of straw in the back. You don't need a lot of muck falling down into that latch before this becomes a problem. No amount of slamming would close it properly.

Sorry it was a few years ago and I can't remember exactly what I did, but from memory I think it involved some partial disassembly and just cleaning it out as best I could. I haven't had the problem since.

 

We had this problem on our '08 about a year ago. Finally discovered a safety pin had found its way in there and was jamming it up inside while masquerading as a part of the mechanism. Was able to extract with needle noise pliers once I figured out that it wasn't supposed to be there. No issues since.