I frequently have trouble manually editing track/take automation. When I try to add nodes nothing happens. I can change the slope of the line between two nodes. I can start playback and write automation with the draw tool or the slider at the right end of the take lane control area, but while playback is stopped I can't manually put in nodes.
 

I just use the smart tool, and allow it to change into the pencil. Then a single click should add a node.
Perhaps you could drop in a screenshot of the troublesome tracks.
Are you using automation lanes or automation on the track?
 
All the best,
 
Lee.

It's just a regular volume automation lane, on an audio track.Nothing to see or be gained by posting a screenshot. Sometimes it's working somemetimes not.
Smart tool or pencil tool, no difference. Mouse click does not insert a node, but right clicking allows me to change a curve. I was thinking some how the track is locked in some way.

Locking tracks has no effect on automation curves, so it's not that.
 
Have you got the edit filter on the track set to the correct envelope?