Fall while walking around rock

On the mountain, climbing the first section and then going to the right, there is a little cavern where you can find a drop and a book. Going out from the cavern an enemy comes from underground, I killed him, then exiting and going right there is a small “road” of rock where you can walk laying the wall.

Well… I tried twice but something blocked me while walking and made me fall before to reach the patform next to it.

Is it a glitch or something?