Sometimes when you have the camera underneath your creation you can't work through the floor. It depends on the distance between camera and floor.
This has been like this since I started playing some weeks ago.

However... Even if the block you're trying to modify doesn't get highlighted (red) sometimes it ís clickable and you can change the settings.
I'm pretty sure sometimes this works with a Suspension block.

So not sure what's the bug, that it's working, or that it's not.