Perhaps you have enabled time remapping or applied a temporal effect, but without more info nobody can tell exactly what you did.
In other words, you are unaware of a feature which allows you to control the position of the current time indicator independently of movement to the next/previous visible area. So, I am probably observing some sort of buggy behavior.
If you're certain that your OS is approved for your version of AE, and your machine meets the System Requirements for that version, you might have a bug. However, I doubt it.
Here's why: I've never, EVER heard about the feature you're alluding to, and I've been using AE since 1996. To my knowledge, there's no such thing as a playhead in AE. There's a CTI and that's it.
I found the reason.
If you display keys as a column in the timeline: Column > Keys, the "key navigator", which I gather is what the vertical line is called, moves independently of the CTI.
To, undo it, stop displaying the key column.
the columns are in the timeline panel menu which can be opened by right clicking on a blank area around the columns, in windows anyway. If you have a one button mouse turn away from the computer and click behind you.