Try Settings, Apps, All, find your keyboard app, then clear cache and data. While you're about it, do a Soft Reset afterwards...Power Off the phone, followed by Restart.
This happened with every one of my Samsung phones and I've about had it to the point of switching to apple. No where in"all"of my apps + Samsung apps can I find a keyboard app so I don't know what its using. I swear it's got me so mad and aggrevated I'm about to get a bat beat the phone and go out and buy an iphone. So please help me fix workout having to do a factory reset. Thanks Christy