My own V22/curve machine middle door can be a bit hard to open too. I have to pull hard on the release.
If you can't get the middle door open by operating the latch release, you will need to reach inside through the belly door and tug on the release cables.
The middle door has a latching mechanism on the right side and left side wall of the cabinet. Reach upward through the belly door opening along the side wall and feel around for a thin steel cable. It will have some slack and may seem a bit loose. Apply a little finger pressure on the cable and the locking latch will pop open. It won't take much force, just light finger pressure and you should hear a click. Do this to each side and the door should open. Once you get the door open, you will need to adjust the cable. Pull the yellow handle on the left inside wall of the cabinet to release the deck, then raise the deck for access. Now will be able to see the cable and adjustment nut. It probably is a bit out of adjustment. Adjust it so it will trigger the latch release.