I've just imported Adventure Creator in another project and I've noticed the Sample Scene with the SamplePlayer3D prefab, the Animator's "Land" parameter is never being triggered. I haven't changed anything with this scene or this prefab. Is this is a known issue?

Comments
The Land trigger's invocation is currently based on the difference height between the Player's Y-positions before/after being in mid-air.
You can adjust this in the Player Land component, but currently a jump on a flat surface won't invoke Land because this height difference will be zero. I'll adjust it so that it's instead based on the difference between the apex of the mid-air position, and their land position, so that it can be enabled for this situation. Thanks for detailing.
Thank you. I anticipate there would be quite a few use cases where folks would jump on a flat surface like a floor, a road, the inside of a house or a factory, etc. Is there a temporary code-fix I could perform to remedy this now?
Replace its Update function with this, and then reduce the "Height Threshold":
That does now initiate the landing animation and triggers that parameter. Thank you so much for taking the time to do this. It did introduce another bug though in that I can now double jump in the air...so there may be some conflict/bad timing with the transitions in the current Animator I'm using.
One issue I've discovered is I have no option to zero out Jump Speed. For instance if I want to remove all jumping, I'd zero out that speed and I cannot. So it seems my option may be hacking it by setting an unusually high simulated mass and lowering Jump Speed to 1.0? Or perhaps removing the Jump input assignment?
Physically double-jumping, or just playing the jump animation in mid-air? I can't recreate either with the Sample Player.
Removing the Jump input assignment is the intended way to disable jumping altogether. To disable it temporarily, use the Player: Constrain Action.