The users tab shows how many tickets each user has (regardless of state).
The tickets (Which by default is the Open) tab shows open tickets that you have access to see.
Comparing the two is like comparing a pomegranate to a steak.
If there are open tickets (and you know that for sure) and you go to open tickets and do not see them then your account does not have access to see tickets the open ticket(s). All tickets are belong to a Department. You would need to add access to that department to your Agent account.