So I was just doing my weekly bike check. I was actually focusing on my chainring bolts because I can hear it starting to creak. So I fixed it. (I don't have to worry about that for another few weeks when they loosen up again.) Back to my story, I also lubed my chain and loosened the tension because it seemed a little tight and I felt like there was a lot of stress down in the drivetrain. The chain is pretty loose now but not too loose, but loose enough where I feel a little play when trackstanding. But when my bike is upside down, and I spin my pedals and leave it spinning, I hear creaking and my pedals and wheel stops spinning really fast, as if my chain is super tight and it's binding. But it's actually pretty loose and well lubricated.

Anyone have an idea what's wrong here?

What kind of play do you feel? What does it feel like?

That play you get from a loose chain tension. I always rode with my chain tension pretty loose. It's not too loose to the point where it's about to fall off my gears. I think the problem lies somewhere else though. =/

Does it creak in a pattern? Like every full rotation of your cranks, if it does, it might be warped chain ring or it could be a chainline issue. This is hard to figure out because we can't see or hear how your bike is behaving. You could try straighten out your chainline and tighten the chain a little bit and see if that'll it.

This.

I would check your bottom bracket or the rear hub

+1

The chain won't influence the bearings in the BB or bearings in the rear wheel hub.

Check tension on chain at different points of the rotation.

Read this: https://sheldonbrown.com/fixed-conversion.html#tension

I'm taking a stab in the dark that the chain is not the culprit. Why would a loose well lubed chain cause the wheel to stop spinning? Makes no sense to me.