Thais, glad to help!
Normally, retrying the upload from scratch should solve the issue. If the issue persists several times such as in your case, it could be that there is some interference. We had some feedback of users who had issues operating in areas with strong wireless networks or electrical pylons. Maybe that applies to where you flew your project and could explain the difficulties in starting the mission.
As for the images not being taken, a check you could make to see if the drone takes images is to switch from the map view to the camera view, then each time a picture is taken, the screen should blink.
Also, this comment from Julie from another post should help explain the situation: https://community.pix4d.com/t/2910-Picture-capture-fail?page=2#community_comment_115004714086&gsc.tab=0