Problem with filtering in the query editor

Hello everyone,

I am a novice in Power BI and have been trying to use the Query Editor in Power BI to load a certain line from multiple files with the same format in a folder (containing multiple subfolders).

I use the 'folder' as a source and then filter so that I only have the xlsx files. Then I filter on a certain part of the path so that only the reports that I need remain. I use custom functions to load the content of the files, and filter on the sheets that I need from each file. After all these steps I end up with these columns:

File name / Column3 / Column10

Column 3 displays names of portfolios and column 10 displays the AUM. Now I need to filter on value 'Total' in column 3, so that I get the total of all portfolios. However, when I do this, it filters out a lot of files that do contain the 'total' value. When I first filter on the filenames, and then on 'total', I do get the total lines of a lot of these files that were missing earlier. Does anybody know what might cause this?