This is a timing issue that isn't really solveable, I would say, in octopus itself.
If your slaves are really that far behind your master, you might need to put in a page that simply says "New User Created" with a "View user option" or something along these lines in order to give your database stack time to catch up. You might also consider caching data in the session and using it after the redirect. Or if the slave query fails fall back to the master? There are several things you could try.