What type of device are you using?
Have you verified the theme is compatible with the Android version you are running on your device?
I could use some more info!
Does clearing the keyboard data/cache help? Try clearing the app's cache or data and then try again.
As well, the device cache might need cleared to help. Try wiping the device cache and then this action again.
I am having the same issue, none of the keyboard aspects of the themes are working. I am using Samsung themes from Samsung store and Samsung keyboard.....this needs to be fixed ASAP