We have started to use the "new" "next-gen" Kanban board. But the "done" column is not cleaned as it is mentioned as "Cards completed more than 14 days are hidden ..." But we can still see the older cards and it looks like there is no way to clean up the DONE column.
What is Attlassian time frame to update that feature? Because current "next-gen" Kanbard boards is useless with the current settings.
Long time Atlassian user is pissed off now. Good to know! 
