This happened to me last night! (Not the crash, but the stuck-ness.)
I have a household of two married couples and their friend. The friend and one of the wives are doing Extreme Sports Enthusiast, while the other three are doing Mount Komorebi Sightseer. They live in the Old Salt House in San Myshuno. The husband of the woman doing Extreme Sports Enthusiast and the other wife are Global Superstars.
So, the woman doing Extreme Sports was the one I used to click the board to start the hike, since she was one of the two I was doing it for. (The other three were just coming For Funsies.)
The three non-famous Sims stood at the top of the stairs and the two Global Superstars did the dumb celebrity walk (sorry) up and down the hill and in circles around the people standing at the top of the stairs. I tried to cancel and couldn't, so I reset object on one of them...
...at which point they teleported to where they should be on the trail and they were all angry with the woman who started the hike and all had a bitter sentiment against her ("terrible hike, got lost"). I was SUPER SALTY because NOT GUILTY.
I fear I used cheats to remove all sentiments from all five of them, yikes. This did, however, count as "completing a hike" for the purposes of their aspiration. :-/ There were also forest spirits near where they ended up but it was like pulling teeth to get them to STOP STANDING AROUND and MAKE A WISH, good grief!
When the two doing Extreme Sports need to survive wildlife attacks I'm going to leave the Sightseers at home. My Extreme Sports woman's celebrity Sightseer husband got a scared buff from the wildlife as it was and would probably concur.
[edited to add] Since you want an unmodded save, I'll see if I can get my latest test user to hike with a friend. Er. I was testing something Completely Other so she might have to MAKE a friend first, lol.
[edited again to add] Interesting. So, as expected, she went hiking, she and Megumi Ito stood at the top of the stairs, then teleported to a spot, then it started raining and she ran but not all the way inside and instead stood outside the Izakaya in a thunderstorm with hiking still in her queue. I'd saved at the start of the hike, so I exited and reloaded the game with the hike in progress... and thus far they're actually walking. They didn't do a complete hike, though, and just walked back and forth in front of the stairs a ways and then Megumi left and she started playing on her phone. So I restarted the hike and again, they're just standing around at the top of the stairs doing nothing.
Here's a video of my test Sim, Megumi Ito, and Geoffrey Landgraab "hiking." https://youtu.be/HbbfDKRZvxM After an inordinately long period of time, they teleported to further along the trail. Then there was a thunderstorm (oddly hilarious). https://youtu.be/Yk2b_78a-WA After the hike, and after the thunderstorm, she did her queued freak-out about the storm. https://youtu.be/QcseJHjQN7E
I've shared my save and the raw video files via PM; I hope that helps!
In the meantime, apparently if you save your game once they're up the stairs and fully exit out, then reload from that point they will walk up and down the trail there and that will count as a "hike."
Issue is still happening on a group hike. Tried loading in to various lots around Senbamachi and tried clicking different hiking board notices. They still get stuck at the top of the stairs. Both adult sims are in my household.
