Cannot edit 2D colliders?

After pressing edit collider on a 2D collider of any kind, mousing over the green collider line does not produce clickable points like it usually does.

I’m not sure how to fix this problem; common solutions were change Z axis, ensure debug mode is off etc.
Has anyone else come across this issue? I feel like I did something wrong somewhere to cause this, but it’s normally pretty straightforward. It’s a fresh project too.

There is an answer here. Might be because of the editor layout.
http://answers.unity3d.com/questions/969724/i-cant-edit-my-collider-cursor-even-if-i-pressed-t.html

I’m having the same issue.
The solution in the thread that UDM1983 linked doesn’t work for me.
This happens even if there’s nothing else in the scene.
But only sometimes.
It usually goes way after a few days, and then returns a few days later.
It’s random. I can’t find a pattern or any specific way to cause it.