Just now, I got stuck [for few seconds : ) ] in the mission where Batman needs to find an alternative path/way/route to the Medical Center/Facility.
When you open the door to enter the MF, you will see a force field and behind it is Harley Quinn: after a short cutscene, you will be required to find an alternative way to enter the MF because of the force field door.
Go outside the door and look above: then press F to reach the top. Now you can go towards the left side: at the end will you see another roof top where you will notice a different brown wall: this is a weak wall that you can take down.
Use the Explo-sive Gell to break this wall. After that, you can continue the game: