When your unit is next to a tall hill or mountain and you try to get it to go to a tile next to that location, sometimes its pathfinding is off where it will go all the way around the mountain instead of 1 or 2 tiles away. Additionally, I've had it where I can't even click on the tile I want to send the unit to, for instance, sending my sovereign to speak to a champion. Zooming in seems to fix this.
Whenever the ability to see the path your unit will take is added, that should also help troubleshooting the problem.
