That's Tableau's way of telling you that you don't have enough room to show the value in that cell.
There are several ways to fix that: you can manually make the columns wider, you can change the font size, you can remove decimals (if there are any), or you can play with the auto-sizing of content by changing the setting from "standard" to "Fit Width" or one of the other options.
Typically the "###" displays instead of data when there is not enough space to display all of the data.
Please try one of the workaround options documented in the article below.
Hope this helps