I'm not following the problem. Is this a normal tooltip or a viz-in-tooltip? What exactly is not showing? Any chance of seeing an example or two?
Hard to troubleshoot with just that description. Not sure if your tables are tables in a database that have been joined, or if you're blending, or if you're talking about data displayed in tables within Tableau.
Missing data sounds like either a filtering issue or a join issue though. I'd check your joins, strings, and make sure there's no type mismatch.