Can you share a screenshot?
If it's not showing any marks, it may be a bug we've been seeing. What version of Tableau are you using?
Either there could be filters applied in the worksheet or the actual sheet might be hidden behind a blank container.
My tableau version is 2018.3.2 (20183.18.1219.1533) 64-bit
I took a screenshot and please see that the March total shows 4, while the details tab only display 3. Unfortunately I had to blur the columns due to confidentiality reasons but you can get the gist hopefully. The issue is that i can see the data when i click into the 4 and all the underlying data shows up but it doesn't show up on the details tab like it's shown here.
Please see the thread as i've provided a screenshot with limited info.