This happens to all slopes. It's because of the speed of flash jump being too fast I presume?

Using FJ facing this wall in subway clips you through the ground too.

Thanks for the clear steps! Flash Jump could carry you far enough in one moment to skip past the start of a slope or the corner of a ledge, so the landing was missed and you dropped into the rock. The jump now checks its whole path, the way the original client does. It's live. Please try Flash Jump facing up the Perion rock slopes and at the Kerning subway walls again, especially on a slower device.