Rigidbodies with single sided colliders no longer work after update

So in my 3D game I have a platform that allows objects coming from below to pass through it, but collides with objects coming from above since it's mesh collider is a quad. Since the platform needs to move, it has a kinematic rigidbody. Before updating unity, any rigidbody objects colliding with this from above behaved as expected, but after the update, rigidbodies only collide with quad shaped mesh colliders if that object does NOT have a rigidbody component, even if it is kinematic. This is in unity version 2020.1.0f1
To replicate create a plane and a sphere. Add a rigidbody to each and make the plane's kinematic. The sphere falls right through the plane.

I'm unsure if this is a bug or some sort of performance improvement, but is there any way to get the platform to collide the way it is supposed to while still being a kinematic rigidbody?

 

As for your description, it looks like a bug. I'd recommend you to create a small project where the issue can be reproduced consistently and submit it via bug report form (Help > Report a bug...).

 

It turns out the bug is fixed in the newest unity version.