connection lost

During my 2nd flight with my Mavic 2 Zoom in the mountains into an open wide valley, I suddenly lost the connection to the drone at 176m (577ft). The picture on my mobile phone (Samsung S8+) was frozen and in black and white. I checked the cabel from the phone to the remote controll it...

Can some one help me "guess" what could've caused this near-miss incident (see attached KLM file). In a nutshell, I launched my Mavic Pro from the hand while ocean fishing on a boat. It flew great for about ~5 minutes...then it freaked out saying it lost connection and began to returned home...

At a flight this evening I lost connection. RTH but didnt reconnect on the flight back. Was only approx 300m away. LED on controller turned red and stayed red. Never happened before. Phone I use has no SIM card and is only used for flying. There might have been some interference in this area but...