Welcome to our forums and thank you for posting. I'm sorry that you've been unable to Catch Up with Criminal Minds.
I'm afraid that On Demand content is made available to us by the broadcasters themselves. We are therefore limited by the licensing agreements and any other terms set out by the content provider. If particular series or episodes have been removed, this would usually be because the license has run out or the broadcaster has decided to remove these from our platform, potentially as well as other locations.
In this case, it looks like Sky may have taken the decision to remove all series for now.