Unable to mark Docker Level 3 as complete

Hi, I cannot mark the Docker Level 3 complete after finishing all tasks. The mouse cursor changes to the red crossed circle when I try to click on the “Mark complete” button:

I and @jorge-humberto-lozan previously reported this issue in the Docker category, but noone has replied yet.

UPDATE: It seems this is a UI bug. After multiple clicks on and around the “Mark Complete” button, I was able somehow activate the button and mark the level as complete.