same here, one of the camp sites spawns the vehicle down below a cliff and you have to base jump to get it, and the parachute dose not work or prompt at all (yes it is unlocked)
Ubisoft has a lot of bugs in this game,
the parachute not working,
the falling animation glitch when you drop off a small ledge to jump off a box or something,
the unable to use/switch gear and pickup or interact with intel / chests bug is borderline game breaking.
this game was not ready for launch at all
my tutorial quests re completing every time I load the game, and many many ui bugs with customizing and breaking down gear.
I've gotten base jumping to work only on rare occasions and never from the same spot consistently. You're supposedly only require to hold space while moving towards the edge of a cliff face, but I've gotten it to work by only standing at the edge and holding space and then never have it work again. I've also had a friend get it to work by mashing the space bar, but I could never get that to work for me. Its as if the game's systems (such as the slope detection system) is actively fighting the base jump mechanic for priority. I also don't understand why there isn't a prompt of any sort. In fact, I don't understand why they didn't just keep the base jumping mechanic from Willands.
More than any of that, I don't know why this isn't listed on their "Known Issues" post.
There is a trick to base jumping. Do not press forward (default W) when jumping. Basically, run toward the ledge while spamming the deploy chute button (default Spacebar) but let go of forward right when you reach ledge. Also, if there is any rock or another lower ledge right below, it wont work, the character will just do the climb down animation.