[Am I asking the right question?]
All issues, even older than 2 weeks appeared on my Kanban board! I used filters before that.
I understand the concept,"It's based on the "Updated" date. It doesn't matter when the issue was completed, if it's updated, it will appear back on the board until the selected "Hide when completed" timeout occurs (again, based on the "Updated" date)." I have checked the solutions online and everything is correct by the book, but still something is missed.
Also, is there any way to check the logs for these kinds of activities?