LOL I feel stupid for asking this, but for some reason everything with RB falls through Terrain.
Terrain has terrain collider, objects have RB and collider (tried box, sphere etc… none of them works). And ofc all colliders are NOT marked as triggers. Any ideas?
Your objects are starting above the terrain and not intersecting it, right? Do an experiment and see if your objects collide properly with a plane? If so then you can isolate the problem to being located in your terrain setup.
“Your objects are starting above the terrain and not intersecting it, right?”
Yup. Testing with 2-3 units above terrain. Everything works fine when i create a new scene.
Edit:
Tried a new terrain in the scene - nothing.
Plane with box collider - still nothing.
Well it works everywhere except for one scene.
That’s odd… new scene works fine? So this is an older scene you’ve been developing with? Could be you’ve got stuff on different layers and you’ve maybe turned off physics collisions for those layers?? Just a thought… but now I’m truly guessing.
OK fixed it - I had a huge skybox sphere w/ sphere collider in the scene. Turning off the collider fixed the issue.
Thanks mate! 
Oh weird! Never would have guessed that. Glad you solved it!