This happens to me all over the board, rpi3, rpi4, different power cables and sources. Doesn't matter. It is not a power issue. Streams do get interrupted and only the audio returns. It started after the big update which is called Matrix. Leia did not have this problem.
I think two "things" lead to that "picture freezing", the imperfect stream (from RPi powered HDD or TVheadend server with interlaced video and limited antenna signal) and the mediaplayer/codec changed after Leia (probably far more sensibile to stream issues).