How should I fix keyboard problems on iOS? Since I started using custom keyboards on iOS (I'm using SwiftKey) I get an intermittent problem whereby Messages freezes. Also, other apps sometimes can't access the keyboard at all.

Is this a recognised bug for iOS 8? Is there a known solution?
Solution? Use the Apple default keyboard.

3rd party keyboards can always have issues and it is up to the vendor to release updates to fix them.

You can post your issue at http://vip.swiftkey.net/index.php?/forum/705-ios-user-to-user-community-support/ and see if someone can help but more than likely you will need to wait for an update.