By now I have have come across several objects ranging from stairs to higher ones which I wasn't able to either walk over or climb up. So far it seems that the steps are too high to just walk over, but too small to enable the climb function. Other examples are concrete blocks where objects might be too close to the edges.

For example in Emelius Port at the north side there are concrete blocks with a fence. As soon as I was standing close to the corner, right where the fence makes a 90 degree turn, I could climb up. Just one step to the left along the fence, I couldn't anymore. I could reproduce that along the whole fence to where it ends in the NE, where the road starts and a turret is positioned. It almost seems that the game thinks that there might not be enough space to climb up.

This is just one example where this would happen.