Just checked "Enforce Unique Values," but my list is still allowing duplicates.

Hello.

My office uses a shared Microsoft List. In an effort to avoid duplicate entries, I checked the "Enforce Unique Values" for the Title.

I tried testing it to see if it works, and the list is still allowing duplicates. 

I've used this feature successfully in the past, so I'm a little confused on why it's not working.

Any ideas? Appreciate any tips/tricks/input 🙂