We will need a .twbx file to look into issue. Please post so that we can help.
This sounds like a scoping issue. The calculation (that which Tableau has generated) will be: Sum(<your field>) / Total(Sum(<your field>))
Total is a window_calc so a scope will need to be defined although, to be dynamic, it is best to apply to the table(down) or table(across) scope.
I'm guessing you are trying to build this (and thus troubleshoot) only against the chart. Please can you duplicate your chart as crosstab and thrn build from there, this way, you will be able to see how the calculation is being applied.
Looking at the charts you have provided, my guess is that there is some dupes / double-counting in your set that is being overlooked in the default view, but then surfaces when you reduce the size of the set as a result of the filtering operation(s).