I had the same thing happen. Those things disappear so fast. Canceling the hike is sort of delayed. It will cancel but the sims continue walking to the next waypoint before stopping. Even cheating and resetting the sims makes them appear at the waypoint. And by the time the sims can get back to where the spirits were, they were gone.
So the way I got it to work so I could collect them is not use hiking and just use the "Go Here Together". The forest spirits also seem to spawn at the same places so once I learned where they spawn, I kept my sims a little bit away and waited. Spent a lot of time waiting so it takes patience. They don't seem to show up on a predicable schedule as far as I can see. To complete both aspirations, you have to do it twice for each sim too. So it felt like it took forever.
Hope this helps.
Same problem for me
