Why is line attached to keyframe missing at the bottom?
The tangent is missing, because this keyframe is not eased. Mark the keyframe, press F9 to apply easyease and you are good to go.
Thank you very much for help.
What is meant by "ease"?
What is meant by "ease" here?
Since the current Keyframe Interpolation of the 1st keyframe is Temporal: Linear, there's no tanget to show.
By pressing F9 (as mentioned in the prior post) while that keyframe is selected, you tell After Effects to apply Animation > Keyframe Assistant > Ease Ease. This changes the Keyframe Interpolation of the 1st keyframe from the Temporal: Linear default to Temporal: Bezier and as such there's a tangent to show.
Thanks for exolanation and link