the name says it all.
version 4.1.7

The name (title) says that you need to provide more information.

Do you have more than one monitor and/or are you using a graphics display tablet?

How do you usually get the Timeline docker showing? What's different about your problem situation? How often is 'sometimes' and is this under any particular circumstances?

Is the Timeline docker showing in the Settings -> Dockers check list? Have you tried the Workspaces dropdown list (far right side of the Toolbar at the top of the screen) and selected the standard Animation workspace?