I have never seen this behavior. Are you new to AE? Is Rotobezier switched on?
Make sure your app is up to date.
I am pretty experienced in Ae but I just switched to CC so the software is up to date. I tried rotobezier on and off. Still won't add a second point and locks on Add Vertex tool. So weird.
That is weird.
Double-check your version number and tell us what it is. We've had a large number of posters recently whose CC software said they were up to date, but it was lying.
Does it behave if you try to make a mask on an AE native solid layer? What about making a shape layer?
And yes, I can make masks on everything with the pen tool except this PSD layer. If I precomp it, I can make a mask on that precomp so I've found a work around, just wanted to find an answer or maybe fix a bug.
That's odd. What happens if you try it on a brand new, completely unrelated PSD layer from a completely unrelated PSD in a completely unrelated project?