Existing categories not listed in dashboard

https://www.gabrielecripezzi.com/nocats.jpg

The Hobbies category looks empty (0 shows in the cats list on the right) but the children categories do exist (see the categories widget at https://www.gabrielecripezzi.com)

This is pretty bad. It happens after I have deleted some categories.

Is there anybody able to help me to fix this?

Thanks a lot!

Gabriele