If you are moving the KinematicBody, try moving it with a non infinite inertia and then it shouldn’t apply a TON of force. It is the last argument in move_and_slide.
For the object being spawned in, if it overlaps then that could be causing the issue because of the collision margin on the collision shape. I would try reducing the margin and seeing if that helps.
Something else you could try as well is changing the RigidBody mode to Static on the non-KinematicBody, swap the KinematicBody, and then set the mode back to Rigid again on the non-KinematicBody. That might help reduce the sudden “it appears” aspect for the physics engine and that in turn may solve the issue.