The {tip} tags are not being converted
The Tooltips plugin is not published
Check if the Tooltips plugin is published. Go to System >> Manage >> Plugins and search for the system plugin System - Regular Labs - Tooltips. Then publish it.
There is markup on the {tip} tags
It is fine to give styles to the title and text within the {tip} tags, like: {tip My Title}
But giving styles to other parts of the tag, or the entire tag, can cause problems, like: {tip My Title}
If you have copy/pasted code directly into your editor, you might also have copied along hidden HTML tags. So this will also cause the {tip} tags to break:
{<span>tip</span> ...}
Remove the extra styling or other html tags around and in the {tip} tags that might cause problems.