Unreliable collisions between StaticBody concave trimesh and RigidBody

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Unreliable collisions between StaticBody concave trimesh and RigidBody

drakeblue

Are Trimesh StaticBody colliders supposed to collide well with other objects that are RigidBody(s)?
Are there known gotchas?

Using Godot 3.4.4, I have a room with a KinematicBody player and a RigidBody object in it (both simple CollisionShapes). I have a simplified mesh of the room's walls that I've added to a MeshInstance and got it to generate a "Trimesh Static Body" so there's a StaticBody and a Collision Shape under the MeshInstance now.

I can move the KinematicBody player around with move_and_slide and it stays within the room reliably so it feels like I've generated the Trimesh okay.

But the RigidBody object falls through the floor. If I reduce the gravity scale on it then it lands okay, but if I push it about with the player it quickly sinks through the floor and keeps falling.
I added a simple cuboid CollisionShape to just be the floor and that stops the object falling through it and then I can push it about with the player. When I do this, so far I haven't been able to push it through the Trimesh walls at all. I could work with this if it's a reliable workaround, but I'm hoping to add a lot of rooms (and might want some with non-flat floors) so if it's not then I'd like to find out soon.

I'm pretty new to Godot so maybe I'm going the wrong way about this entirely? Should I break up the room trimesh collider into convex shapes e.g. for walls, floor, ceiling rather than use a single mesh?

I looked here, but couldn't work out if it says that what I'm trying is supposed to work or not:
https://docs.godotengine.org/en/stable/tutorials/physics/collision_shapes_3d.html

Any help appreciated, thanks.