Filter Pane - sort order and show hierarchy

AndreaZenner did you find a solution?

I'm having issues with the filters pane sorting order!

I have a calculated column to get the 1rst letter of the client name. All works well. Except that  when the column is pinned to the filters pane, it is not displayed in alphabetical order.

It shows like below 

However, when I select the column and select filter by, the order is correct!!!

Having the column pinned to the filters pane and displayed by default, is a requirement so the users have a better experience.

I've recreated the view, save it, reorder the column. But nothing seems to work.

I would appreciate any suggestions.

Thank you in advance