Help clock widget invisible


I have a small but really annoying problem on my samsung galaxy s3 mini. I'm trying to add a clock widget (which had frozen before and which I removed), but when I add it to any of my screens, it doesn't show up. It's invisible. On the other hand, I know there's a widget there, because I can select it and remove it.

Any suggestions as to how, I don't know, clear some caches or something?