Medal not appearing in medal tab?

Describe the problem. Be as specific as possible!:
Last night, I got the Horntail Slayer title. I had 36 medals in my medal tab, and I checked earlier and it was still 36. Now, it says I only have 35 medals, and the Horntail Slayer medal is still in my inventory.

I double clicked myself, and it says I have 37 medals under the collection tab. There, it shows the Horntail Slayer medal, and another one that I didn't notice was missing - the Diligent Explorer medal.

 Images of problem

Medals are sorted alphabetically. As you can see, there is no Horntail Slayer title there, even though I have it in my inventory.