Description:

    1. When I use repeating command block and input "/ride [player] mount [UUID]", I can ride on the entity once. Then, I'll fall off from the entity, and I can move freely. When I press SHIFT, I'll replay the animation of fell off from the entity.

    2. After I used repeating cb and fell off, when I place blocks, I can't place at where I pointed at. The block will be placed elsewhere. 

    3. The description 2 is like that the player I am controlling is a fake person, the true player is on the entity I am riding.

Recreate:

    1. Place a repeating command block and an entity(armor stand in my video).

    2. Copy "/ride [player] mount [UUID]" to the command block.

    3. Active the command block.

    4. The things I describe above will happen.