DJI Spark,Android,camera problem

Hello! I have looked at the support site, but I didn't find something similar. I have an Android phone with Pix4Dcapture installed in it. Also a DJI Spark with its RC. Before 2-3 months I made a freeflight mission with no problem. These days I am trying to launch a mission, but I have no camera connection (just black screen in camera window) although during the checking before the mission starts, the camera is ok. When I fly the drone, it takes every X meters pictures,the RC can move the camera in any direction, but if I can't see on my mobile phone what is capturing, it is a free flight on very hard mode. Can you provide me with some options to check, so I can fix my problem?