Falling Grind Disable
By performing a handplant almost parallel to a halfpipe rail, and then holding the direction opposite the halfpipe, you can put your character in a weird state where they are unable to fall into a grind. You can still jump onto a rail and grind normally, however falling onto ramp rails and similar rails will not function properly. You can cancel this trick by dropping onto the halfpipe floor.
Although not much is known about this trick, what is likely happening is that the game begins either a handplant state or some sort of halfpipe grind state, but gets interrupted by the 1-frame grind after the weird handplant, resulting in the state being stuck until you finish a halfpipe grind normally.