For me....the only time it doesn't show is when I have a different window "active" and then.....sometimes it still shows
Here is an example:
I working away in Solidworks (Solidworks is my active window), and mouse over a button....tool tip appears. All is good.
Then I move my mouse over to my other screen and check my email and other things.
Now, my email window is active.
Then, without clicking anything, I move my moue back over Solidworks....and while the buttons still highlight, no tool tip appears. (although I can get one to appear right now, even though it isn't the active window...LOL) I remember this happening a lot in SW 2015.....but now that I am in SW 2017.....I don't think that it has happened. By that I specifically mean that the tool tip show up all the time now.