(3D) How can I make the player not able to tumble stuff down?

Question

Warning, lots of text incoming!

Hello everyone! I'm making a game that involves platforms that collapse when an object hits it, like a boulder. However, I have two issues;

Bug #1:

Whenever the player collides with a platform that has been hit by a block or another platform, the player can unbalance it. I have tried removing the mask and layer collision for the platform and pole holding it, but to no avail.

Increasing gravity makes the platforms jitter a bit, and I use "Is Sleeping" to make sure that the player (A KinematicBody) doesn't make it tumble if the platform hasn't collided with a rigid body anything.

Bug #2:

I suspect that if bug #1 is fixed, it should fix #2. The problem is similar to the first one, and that the player can push everything.

Here is the player code (Which is a bit old, but works):

    extends KinematicBody

# Cameras
var view_sensitivity = 1.5 / 10
var camera_angle = 0
var camera_change = Vector2()

# Vectors
var velocity = Vector3()
var direction = Vector3()

# Moving
var gravity = -9.8 * 3
const MAX_SPEED = 5
const MAX_RUNNING_SPEED = 10
const MAX_CROUCHING_SPEED = 2
const ACCEL = 10
const DEACCEL = 10
var jump_height = 10
var canSprint = true

func _ready():
    $PlayerMesh.hide()

func _physics_process(delta):
    walk(delta)

# The chunk of code that makes the player move.
func walk(delta):
    var speed

    direction = Vector3()

    var aim = $Head/Camera.get_global_transform().basis

    # Walking
    if Input.is_action_pressed("move_up"):
        direction -= aim.z
    if Input.is_action_pressed("move_down"):
        direction += aim.z
    if Input.is_action_pressed("move_left"):
        direction -= aim.x
    if Input.is_action_pressed("move_right"):
        direction += aim.x

    direction.y = 0
    direction = direction.normalized()

    speed = MAX_SPEED

    direction = direction.normalized()

    velocity.y += gravity * delta

    var temp_velocity = velocity
    temp_velocity.y = 0

    if Input.is_action_pressed("move_sprint") && canSprint:
        speed = MAX_RUNNING_SPEED

    var target = direction * speed

    var acceleration
    if direction.dot(temp_velocity) > 0:
        acceleration = ACCEL
    else:
        acceleration = DEACCEL

    temp_velocity = temp_velocity.linear_interpolate(target, acceleration * delta)

    velocity.x = temp_velocity.x
    velocity.z = temp_velocity.z

    velocity = move_and_slide(velocity, Vector3(0, 1, 0))

    if Input.is_action_pressed("move_jump") && is_on_floor():
        velocity.y = jump_height

func death():
    pass

func _input(event):

    if event is InputEventMouseMotion:
        $Head.rotate_y(-deg2rad(event.relative.x * view_sensitivity))
        Input.set_mouse_mode(Input.MOUSE_MODE_CAPTURED)

        var change = -event.relative.y * view_sensitivity
        if change + camera_angle < 90 and change + camera_angle > -90:
            $Head/Camera.rotate_x(deg2rad(change))
            camera_angle += change